Given a list of numbers, return whether any two sums to k. For example, given [10, 15, 3, 7] and k of 17, return true since 10 + 7 is 17.
Bonus: Can you do this in one pass?
Solution (AllPairsEqualValue.java)
This problem was asked by Uber.
Given an array of integers, return a new array such that each element at index i of the new array is the product of all the numbers in the original array except the one at i.
For example, if our input was [1, 2, 3, 4, 5], the expected output would be [120, 60, 40, 30, 24]. If our input was [3, 2, 1], the expected output would be [2, 3, 6].
Follow-up: what if you can't use division?
This problem was asked by Google.
Given the root to a binary tree, implement serialize(root), which serializes the tree into a string, and deserialize(s), which deserializes the string back into the tree.
This problem was asked by Stripe.
Given an array of integers, find the first missing positive integer in linear time and constant space. In other words, find the lowest positive integer that does not exist in the array. The array can contain duplicates and negative numbers as well.
For example, the input [3, 4, -1, 1] should give 2. The input [1, 2, 0] should give 3.
You can modify the input array in-place.
This problem was asked by Google.
An XOR linked list is a more memory efficient doubly linked list. Instead of each node holding next and prev fields, it holds a field named both, which is an XOR of the next node and the previous node. Implement an XOR linked list; it has an add(element) which adds the element to the end, and a get(index) which returns the node at index.
If using a language that has no pointers (such as Python), you can assume you have access to get_pointer and dereference_pointer functions that converts between nodes and memory addresses.
class Node:
def __init__(self, data):
self.data = data
self.both = id(data)
def __repr__(self):
return str(self.data)
a = Node("a")
b = Node("b")
c = Node("c")
d = Node("d")
e = Node("e")
# id_map simulates object pointer values
id_map = dict()
id_map[id("a")] = a
id_map[id("b")] = b
id_map[id("c")] = c
id_map[id("d")] = d
id_map[id("e")] = e
class LinkedList:
def __init__(self, node):
self.head = node
self.tail = node
self.head.both = 0
self.tail.both = 0
def add(self, element):
self.tail.both ^= id(element.data)
element.both = id(self.tail.data)
self.tail = element
def get(self, index):
prev_node_address = 0
result_node = self.head
for i in range(index):
next_node_address = prev_node_address ^ result_node.both
prev_node_address = id(result_node.data)
result_node = id_map[next_node_address]
return result_node.data
llist = LinkedList(c)
llist.add(d)
llist.add(e)
llist.add(a)
assert llist.get(0) == "c"
assert llist.get(1) == "d"
assert llist.get(2) == "e"
assert llist.get(3) == "a"This problem was asked by Facebook.
Given the mapping a = 1, b = 2, ... z = 26, and an encoded message, count the number of ways it can be decoded.
For example, the message '111' would give 3, since it could be decoded as 'aaa', 'ka', and 'ak'.
You can assume that the messages are decodable. For example, '001' is not allowed.
This problem was asked by Google.
A unival tree (which stands for "universal value") is a tree where all nodes under it have the same value.
Given the root to a binary tree, count the number of unival subtrees.
For example, the following tree has 5 unival subtrees:
0
/ \
1 0
/ \
1 0
/ \
1 1
This problem was asked by Airbnb.
Given a list of integers, write a function that returns the largest sum of non-adjacent numbers. Numbers can be 0 or negative.
For example, [2, 4, 6, 8] should return 12, since we pick 4 and 8. [5, 1, 1, 5] should return 10, since we pick 5 and 5.
This problem was asked by Apple.
Implement a job scheduler which takes in a function f and an integer n, and calls f after n milliseconds.
from time import sleep
def sample_function():
print("hello")
def schedule_function(f, delay_in_ms):
delay_in_s = delay_in_ms / 1000
sleep(delay_in_s)
f()
schedule_function(sample_function, 10000)This problem was asked by Twitter.
Implement an autocomplete system. That is, given a query string s and a set of all possible query strings, return all strings in the set that have s as a prefix.
For example, given the query string de and the set of strings [dog, deer, deal], return [deer, deal].
Hint: Try preprocessing the dictionary into a more efficient data structure to speed up queries.
This problem was asked by Amazon.
There exists a staircase with N steps, and you can climb up either 1 or 2 steps at a time. Given N, write a function that returns the number of unique ways you can climb the staircase. The order of the steps matters.
For example, if N is 4, then there are 5 unique ways:
1, 1, 1, 1
2, 1, 1
1, 2, 1
1, 1, 2
2, 2
What if, instead of being able to climb 1 or 2 steps at a time, you could climb any number from a set of positive integers X? For example, if X = {1, 3, 5}, you could climb 1, 3, or 5 steps at a time.
This problem was asked by Amazon.
Given an integer k and a string s, find the length of the longest substring that contains at most k distinct characters.
For example, given s = "abcba" and k = 2, the longest substring with k distinct characters is "bcb".
This problem was asked by Google.
The area of a circle is defined as r^2. Estimate \pi to 3 decimal places using a Monte Carlo method.
Hint: The basic equation of a circle is x^2 + y^2 = r^2.
This problem was asked by Facebook.
Given a stream of elements too large to store in memory, pick a random element from the stream with uniform probability.
This problem was asked by Twitter.
You run an e-commerce website and want to record the last N order ids in a log. Implement a data structure to accomplish this, with the following API:
record(order_id): adds the order_id to the log get_last(i): gets the ith last element from the log. i is guaranteed to be smaller than or equal to N. You should be as efficient with time and space as possible.
This problem was asked by Google.
Suppose we represent our file system by a string in the following manner:
The string "dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext" represents:
dir
subdir1
subdir2
file.ext
The directory dir contains an empty sub-directory subdir1 and a sub-directory subdir2 containing a file file.ext.
The string "dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext" represents:
dir
subdir1
file1.ext
subsubdir1
subdir2
subsubdir2
file2.ext
The directory dir contains two sub-directories subdir1 and subdir2. subdir1 contains a file file1.ext and an empty second-level sub-directory subsubdir1. subdir2 contains a second-level sub-directory subsubdir2 containing a file file2.ext.
We are interested in finding the longest (number of characters) absolute path to a file within our file system. For example, in the second example above, the longest absolute path is "dir/subdir2/subsubdir2/file2.ext", and its length is 32 (not including the double quotes).
Given a string representing the file system in the above format, return the length of the longest absolute path to a file in the abstracted file system. If there is no file in the system, return 0.
This problem was asked by Google.
Given an array of integers and a number k, where 1 <= k <= length of the array, compute the maximum values of each subarray of length k.
For example, given array = [10, 5, 2, 7, 8, 7] and k = 3, we should get: [10, 7, 8, 8], since:
10 = max(10, 5, 2)
7 = max(5, 2, 7)
8 = max(2, 7, 8)
8 = max(7, 8, 7)
Do this in O(n) time and O(k) space. You can modify the input array in-place and you do not need to store the results. You can simply print them out as you compute them.
This problem was asked by Facebook.
A builder is looking to build a row of N houses that can be of K different colors. He has a goal of minimizing cost while ensuring that no two neighboring houses are of the same color.
Given an N by K matrix where the nth row and kth column represents the cost to build the nth house with kth color, return the minimum cost which achieves this goal.
This problem was asked by Google.
Given two singly linked lists that intersect at some point, find the intersecting node. The lists are non-cyclical.
For example, given A = 3 -> 7 -> 8 -> 10 and B = 99 -> 1 -> 8 -> 10, return the node with value 8.
In this example, assume nodes with the same value are the exact same node objects.
Do this in O(M + N) time (where M and N are the lengths of the lists) and constant space.
This problem was asked by Snapchat.
Given an array of time intervals (start, end) for classroom lectures (possibly overlapping), find the minimum number of rooms required.
For example, given [(30, 75), (0, 50), (60, 150)], you should return 2.
This problem was asked by Microsoft.
Given a dictionary of words and a string made up of those words (no spaces), return the original sentence in a list. If there is more than one possible reconstruction, return any of them. If there is no possible reconstruction, then return null.
For example, given the set of words 'quick', 'brown', 'the', 'fox', and the string "thequickbrownfox", you should return ['the', 'quick', 'brown', 'fox'].
Given the set of words 'bed', 'bath', 'bedbath', 'and', 'beyond', and the string "bedbathandbeyond", return either ['bed', 'bath', 'and', 'beyond] or ['bedbath', 'and', 'beyond'].
This problem was asked by Google.
You are given an M by N matrix consisting of booleans that represents a board. Each True boolean represents a wall. Each False boolean represents a tile you can walk on.
Given this matrix, a start coordinate, and an end coordinate, return the minimum number of steps required to reach the end coordinate from the start. If there is no possible path, then return null. You can move up, left, down, and right. You cannot move through walls. You cannot wrap around the edges of the board.
For example, given the following board:
[[f, f, f, f],
[t, t, f, t],
[f, f, f, f],
[f, f, f, f]]
and start = (3, 0) (bottom left) and end = (0, 0) (top left), the minimum number of steps required to reach the end is 7, since we would need to go through (1, 2) because there is a wall everywhere else on the second row.
This problem was asked by Google.
Implement locking in a binary tree. A binary tree node can be locked or unlocked only if all of its descendants or ancestors are not locked.
Design a binary tree node class with the following methods:
is_locked, which returns whether the node is locked lock, which attempts to lock the node. If it cannot be locked, then it should return false. Otherwise, it should lock it and return true. unlock, which unlocks the node. If it cannot be unlocked, then it should return false. Otherwise, it should unlock it and return true. You may augment the node to add parent pointers or any other property you would like. You may assume the class is used in a single-threaded program, so there is no need for actual locks or mutexes. Each method should run in O(h), where h is the height of the tree.
This problem was asked by Facebook.
Implement regular expression matching with the following special characters:
- . (period) which matches any single character
- * (asterisk) which matches zero or more of the preceding element That is, implement a function that takes in a string and a valid regular expression and returns whether or not the string matches the regular expression.
For example, given the regular expression "ra." and the string "ray", your function should return true. The same regular expression on the string "raymond" should return false.
Given the regular expression ".*at" and the string "chat", your function should return true. The same regular expression on the string "chats" should return false.
This problem was asked by Google.
Given a singly linked list and an integer k, remove the kth last element from the list. k is guaranteed to be smaller than the length of the list.
The list is very long, so making more than one pass is prohibitively expensive.
Do this in constant space and in one pass.
This problem was asked by Facebook.
Given a string of round, curly, and square open and closing brackets, return whether the brackets are balanced (well-formed).
For example, given the string "([])", you should return true.
Given the string "([)]" or "((()", you should return false.
This problem was asked by Palantir.
Write an algorithm to justify text. Given a sequence of words and an integer line length k, return a list of strings which represents each line, fully justified.
More specifically, you should have as many words as possible in each line. There should be at least one space between each word. Pad extra spaces when necessary so that each line has exactly length k. Spaces should be distributed as equally as possible, with the extra spaces, if any, distributed starting from the left.
If you can only fit one word on a line, then you should pad the right-hand side with spaces.
Each word is guaranteed not to be longer than k.
For example, given the list of words ["the", "quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog"] and k = 16, you should return the following:
["the quick brown", # 1 extra space on the left "fox jumps over", # 2 extra spaces distributed evenly "the lazy dog"] # 4 extra spaces distributed evenly
This problem was asked by Amazon.
Run-length encoding is a fast and simple method of encoding strings. The basic idea is to represent repeated successive characters as a single count and character. For example, the string "AAAABBBCCDAA" would be encoded as "4A3B2C1D2A".
Implement run-length encoding and decoding. You can assume the string to be encoded have no digits and consists solely of alphabetic characters. You can assume the string to be decoded is valid.
You are given an array of non-negative integers that represents a two-dimensional elevation map where each element is unit-width wall and the integer is the height. Suppose it will rain and all spots between two walls get filled up.
Compute how many units of water remain trapped on the map in O(N) time and O(1) space.
For example, given the input [2, 1, 2], we can hold 1 unit of water in the middle.
Given the input [3, 0, 1, 3, 0, 5], we can hold 3 units in the first index, 2 in the second, and 3 in the fourth index (we cannot hold 5 since it would run off to the left), so we can trap 8 units of water.
This problem was asked by Google.
The edit distance between two strings refers to the minimum number of character insertions, deletions, and substitutions required to change one string to the other. For example, the edit distance between "kitten" and "sitting" is three: substitute the "k" for "s", substitute the "e" for "i", and append a "g".
Given two strings, compute the edit distance between them.
This problem was asked by Jane Street.
Suppose you are given a table of currency exchange rates, represented as a 2D array. Determine whether there is a possible arbitrage: that is, whether there is some sequence of trades you can make, starting with some amount A of any currency, so that you can end up with some amount greater than A of that currency.
There are no transaction costs and you can trade fractional quantities.
from math import log
def arbitrage(table):
transformed_graph = [[-log(edge) for edge in row] for row in table]
# Pick any source vertex -- we can run Bellman-Ford from any vertex and
# get the right result
source = 0
n = len(transformed_graph)
min_dist = [float('inf')] * n
min_dist[source] = 0
# Relax edges |V - 1| times
for _ in range(n - 1):
for v in range(n):
for w in range(n):
if min_dist[w] > min_dist[v] + transformed_graph[v][w]:
min_dist[w] = min_dist[v] + transformed_graph[v][w]
# If we can still relax edges, then we have a negative cycle
for v in range(n):
for w in range(n):
if min_dist[w] > min_dist[v] + transformed_graph[v][w]:
return True
return False
assert arbitrage([[1, 2], [2, 1]])
assert not arbitrage([[1, 1], [1, 1]])This problem was asked by Microsoft.
Compute the running median of a sequence of numbers. That is, given a stream of numbers, print out the median of the list so far on each new element.
Recall that the median of an even-numbered list is the average of the two middle numbers.
For example, given the sequence [2, 1, 5, 7, 2, 0, 5], your algorithm should print out:
2
1.5
2
3.5
2
2
2
This problem was asked by Quora.
Given a string, find the palindrome that can be made by inserting the fewest number of characters as possible anywhere in the word. If there is more than one palindrome of minimum length that can be made, return the lexicographically earliest one (the first one alphabetically).
For example, given the string "race", you should return "ecarace", since we can add three letters to it (which is the smallest amount to make a palindrome). There are seven other palindromes that can be made from "race" by adding three letters, but "ecarace" comes first alphabetically.
As another example, given the string "google", you should return "elgoogle".
This problem was asked by Google.
Given an array of strictly the characters 'R', 'G', and 'B', segregate the values of the array so that all the Rs come first, the Gs come second, and the Bs come last. You can only swap elements of the array.
Do this in linear time and in-place.
For example, given the array ['G', 'B', 'R', 'R', 'B', 'R', 'G'], it should become ['R', 'R', 'R', 'G', 'G', 'B', 'B'].
This problem was asked by Dropbox.
Given the root to a binary search tree, find the second largest node in the tree.
This problem was asked by Google.
The power set of a set is the set of all its subsets. Write a function that, given a set, generates its power set.
For example, given the set {1, 2, 3}, it should return {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}}.
You may also use a list or array to represent a set.
This problem was asked by Microsoft.
You have an N by N board. Write a function that, given N, returns the number of possible arrangements of the board where N queens can be placed on the board without threatening each other, i.e. no two queens share the same row, column, or diagonal.
This problem was asked by Dropbox.
Conway's Game of Life takes place on an infinite two-dimensional board of square cells. Each cell is either dead or alive, and at each tick, the following rules apply:
Any live cell with less than two live neighbours dies. Any live cell with two or three live neighbours remains living. Any live cell with more than three live neighbours dies. Any dead cell with exactly three live neighbours becomes a live cell. A cell neighbours another cell if it is horizontally, vertically, or diagonally adjacent.
Implement Conway's Game of Life. It should be able to be initialized with a starting list of live cell coordinates and the number of steps it should run for. Once initialized, it should print out the board state at each step. Since it's an infinite board, print out only the relevant coordinates, i.e. from the top-leftmost live cell to bottom-rightmost live cell.
You can represent a live cell with an asterisk * and a dead cell with a dot ..
This problem was asked by Google.
Given an array of integers where every integer occurs three times except for one integer, which only occurs once, find and return the non-duplicated integer.
For example, given [6, 1, 3, 3, 3, 6, 6], return 1. Given [13, 19, 13, 13], return 19.
Do this in
This problem was asked by Facebook.
Given an unordered list of flights taken by someone, each represented as (origin, destination) pairs, and a starting airport, compute the person's itinerary. If no such itinerary exists, return null. If there are multiple possible itineraries, return the lexicographically smallest one. All flights must be used in the itinerary.
For example, given the list of flights [('SFO', 'HKO'), ('YYZ', 'SFO'), ('YUL', 'YYZ'), ('HKO', 'ORD')] and starting airport 'YUL', you should return the list ['YUL', 'YYZ', 'SFO', 'HKO', 'ORD'].
Given the list of flights [('SFO', 'COM'), ('COM', 'YYZ')] and starting airport 'COM', you should return null.
Given the list of flights [('A', 'B'), ('A', 'C'), ('B', 'C'), ('C', 'A')] and starting airport 'A', you should return the list ['A', 'B', 'C', 'A', 'C'] even though ['A', 'C', 'A', 'B', 'C'] is also a valid itinerary. However, the first one is lexicographically smaller.
This problem was asked by Google.
Given a list of integers S and a target number k, write a function that returns a subset of S that adds up to k. If such a subset cannot be made, then return null.
Integers can appear more than once in the list. You may assume all numbers in the list are positive.
For example, given S = [12, 1, 61, 5, 9, 2] and k = 24, return [12, 9, 2, 1] since it sums up to 24.
This problem was asked by Amazon.
Implement a stack that has the following methods:
push(val), which pushes an element onto the stackpop(), which pops off and returns the topmost element of the stack. If there are no elements in the stack, then it should throw an error or return null.max(), which returns the maximum value in the stack currently. If there are no elements in the stack, then it should throw an error or return null.
Each method should run in constant time.
This problem was asked by Google.
We can determine how "out of order" an array A is by counting the number of inversions it has. Two elements A[i] and A[j] form an inversion if A[i] > A[j] but i < j. That is, a smaller element appears after a larger element.
Given an array, count the number of inversions it has. Do this faster than O(N^2) time.
You may assume each element in the array is distinct.
For example, a sorted list has zero inversions. The array [2, 4, 1, 3, 5] has three inversions: (2, 1), (4, 1), and (4, 3). The array [5, 4, 3, 2, 1] has ten inversions: every distinct pair forms an inversion.
This problem was asked by Amazon.
Given a string, find the longest palindromic contiguous substring. If there are more than one with the maximum length, return any one.
For example, the longest palindromic substring of "aabcdcb" is "bcdcb". The longest palindromic substring of "bananas" is "anana".
This problem was asked by Facebook.
Given a array of numbers representing the stock prices of a company in chronological order, write a function that calculates the maximum profit you could have made from buying and selling that stock once. You must buy before you can sell it.
For example, given [9, 11, 8, 5, 7, 10], you should return 5, since you could buy the stock at 5 dollars and sell it at 10 dollars.
This problem was asked by Google.
Given pre-order and in-order traversals of a binary tree, write a function to reconstruct the tree.
For example, given the following preorder traversal:
[a, b, d, e, c, f, g]
And the following inorder traversal:
[d, b, e, a, f, c, g]
You should return the following tree:
a
/ \
b c
/ \ / \
d e f g
This problem was asked by Amazon.
Given an array of numbers, find the maximum sum of any contiguous subarray of the array.
For example, given the array [34, -50, 42, 14, -5, 86], the maximum sum would be 137, since we would take elements 42, 14, -5, and 86.
Given the array [-5, -1, -8, -9], the maximum sum would be 0, since we would not take any elements.
Do this in O(N) time.
This problem was asked by Microsoft.
Suppose an arithmetic expression is given as a binary tree. Each leaf is an integer and each internal node is one of '+', '−', '∗', or '/'.
Given the root to such a tree, write a function to evaluate it.
For example, given the following tree:
*
/ \
+ +
/ \ / \
3 2 4 5
You should return 45, as it is (3 + 2) * (4 + 5).
This problem was asked by Facebook.
Given a function that generates perfectly random numbers between 1 and k (inclusive), where k is an input, write a function that shuffles a deck of cards represented as an array using only swaps.
It should run in O(N) time.
Hint: Make sure each one of the 52! permutations of the deck is equally likely.
This problem was asked by Google.
Implement an LRU (Least Recently Used) cache. It should be able to be initialized with a cache size n, and contain the following methods:
set(key, value): sets key to value. If there are already n items in the cache and we are adding a new item, then it should also remove the least recently used item. get(key): gets the value at key. If no such key exists, return null. Each operation should run in O(1) time.
This problem was asked by Apple.
Implement a queue using two stacks. Recall that a queue is a FIFO (first-in, first-out) data structure with the following methods: enqueue, which inserts an element into the queue, and dequeue, which removes it.
This problem was asked by Microsoft.
Implement a URL shortener with the following methods:
shorten(url), which shortens the url into a six-character alphanumeric string, such as zLg6wl. restore(short), which expands the shortened string into the original url. If no such shortened string exists, return null. Hint: What if we enter the same URL twice?
This problem was asked by Google.
Given an undirected graph represented as an adjacency matrix and an integer k, write a function to determine whether each vertex in the graph can be colored such that no two adjacent vertices share the same color using at most k colors. Solution
This problem was asked by Amazon.
Given a string s and an integer k, break up the string into multiple texts such that each text has a length of k or less. You must break it up so that words don't break across lines. If there's no way to break the text up, then return null.
You can assume that there are no spaces at the ends of the string and that there is exactly one space between each word.
For example, given the string "the quick brown fox jumps over the lazy dog" and k = 10, you should return: ["the quick", "brown fox", "jumps over", "the lazy", "dog"]. No string in the list has a length of more than 10.
This problem was asked by Amazon.
An sorted array of integers was rotated an unknown number of times.
Given such an array, find the index of the element in the array in faster than linear time. If the element doesn't exist in the array, return null.
For example, given the array [13, 18, 25, 2, 8, 10] and the element 8, return 4 (the index of 8 in the array).
You can assume all the integers in the array are unique.
This problem was asked by Google.
Implement a file syncing algorithm for two computers over a low-bandwidth network. What if we know the files in the two computers are mostly the same? Solution
This problem was asked by Facebook.
Given a multiset of integers, return whether it can be partitioned into two subsets whose sums are the same.
For example, given the multiset {15, 5, 20, 10, 35, 15, 10}, it would return true, since we can split it up into {15, 5, 10, 15, 10} and {20, 35}, which both add up to 55.
Given the multiset {15, 5, 20, 10, 35}, it would return false, since we can't split it up into two subsets that add up to the same sum. Solution
This problem was asked by Google.
Implement integer exponentiation. That is, implement the pow(x, y) function, where x and y are integers and returns x^y.
Do this faster than the naive method of repeated multiplication.
For example, pow(2, 10) should return 1024. Solution
This problem was asked by Facebook.
There is an N by M matrix of zeroes. Given N and M, write a function to count the number of ways of starting at the top-left corner and getting to the bottom-right corner. You can only move right or down.
For example, given a 2 by 2 matrix, you should return 2, since there are two ways to get to the bottom-right:
Right, then down Down, then right Given a 5 by 5 matrix, there are 70 ways to get to the bottom-right. Solution
This problem was asked by Microsoft.
Given a 2D matrix of characters and a target word, write a function that returns whether the word can be found in the matrix by going left-to-right, or up-to-down.
For example, given the following matrix:
[['F', 'A', 'C', 'I'],
['O', 'B', 'Q', 'P'],
['A', 'N', 'O', 'B'],
['M', 'A', 'S', 'S']]
and the target word 'FOAM', you should return true, since it's the leftmost column. Similarly, given the target word 'MASS', you should return true, since it's the last row. Solution
This problem was asked by Google.
A knight's tour is a sequence of moves by a knight on a chessboard such that all squares are visited once.
Given N, write a function to return the number of knight's tours on an N by N chessboard.
This problem was asked by Amazon.
Given a N by M matrix of numbers, print out the matrix in a clockwise spiral.
For example, given the following matrix:
[[1, 2, 3, 4, 5],
[6, 7, 8, 9, 10],
[11, 12, 13, 14, 15],
[16, 17, 18, 19, 20]]
You should print out the following:
1, 2, 3, 4, 5, 10, 15, 20, 19, 18, 17, 16, 11, 6, 7, 8, 9, 14, 13, 12
This problem was asked by Google.
Implement an LFU (Least Frequently Used) cache. It should be able to be initialized with a cache size n, and contain the following methods:
set(key, value): sets key to value. If there are already n items in the cache and we are adding a new item, then it should also remove the least frequently used item. If there is a tie, then the least recently used key should be removed.
get(key): gets the value at key. If no such key exists, return null.
Each operation should run in O(1) time.```
This problem was asked by Google.
On our special chessboard, two bishops attack each other if they share the same diagonal. This includes bishops that have another bishop located between them, i.e. bishops can attack through pieces.
You are given N bishops, represented as (row, column) tuples on a M by M chessboard. Write a function to count the number of pairs of bishops that attack each other. The ordering of the pair doesn't matter: (1, 2) is considered the same as (2, 1).
For example, given M = 5 and the list of bishops:
(0, 0)
(1, 2)
(2, 2)
(4, 0)
The board would look like this:
[b 0 0 0 0]
[0 0 b 0 0]
[0 0 b 0 0]
[0 0 0 0 0]
[b 0 0 0 0]
You should return 2, since bishops 1 and 3 attack each other, as well as bishops 3 and 4.
This problem was asked by Facebook.
Given a list of integers, return the largest product that can be made by multiplying any three integers.
For example, if the list is [-10, -10, 5, 2], we should return 500, since that's -10 * -10 * 5.
You can assume the list has at least three integers.
A number is considered perfect if its digits sum up to exactly 10.
Given a positive integer n, return the n-th perfect number.
For example, given 1, you should return 19. Given 2, you should return 28.
This problem was asked by Google.
In a directed graph, each node is assigned an uppercase letter. We define a path's value as the number of most frequently-occurring letter along that path. For example, if a path in the graph goes through "ABACA", the value of the path is 3, since there are 3 occurrences of 'A' on the path.
Given a graph with n nodes and m directed edges, return the largest value path of the graph. If the largest value is infinite, then return null.
The graph is represented with a string and an edge list. The i-th character represents the uppercase letter of the i-th node. Each tuple in the edge list (i, j) means there is a directed edge from the i-th node to the j-th node. Self-edges are possible, as well as multi-edges.
For example, the following input graph:
ABACA
[(0, 1),
(0, 2),
(2, 3),
(3, 4)]
Would have maximum value 3 using the path of vertices [0, 2, 3, 4], (A, A, C, A).
The following input graph:
A
[(0, 0)]
Should return null, since we have an infinite loop.
This problem was asked by Google.
Given the head of a singly linked list, reverse it in-place.
This problem was asked by Apple.
Suppose you have a multiplication table that is N by N. That is, a 2D array where the value at the i-th row and j-th column is (i + 1) * (j + 1) (if 0-indexed) or i * j (if 1-indexed).
Given integers N and X, write a function that returns the number of times X appears as a value in an N by N multiplication table.
For example, given N = 6 and X = 12, you should return 4, since the multiplication table looks like this:
1 2 3 4 5 6
2 4 6 8 10 12
3 6 9 12 15 18
4 8 12 16 20 24
5 10 15 20 25 30
6 12 18 24 30 36
And there are 4 12's in the table. Solution
This problem was asked by Microsoft.
Given an array of numbers, find the length of the longest increasing subsequence in the array. The subsequence does not necessarily have to be contiguous.
For example, given the array
[0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15],
the longest increasing subsequence has length 6: it is 0, 2, 6, 9, 11, 15.
This problem was asked by Google.
You are given an N by M 2D matrix of lowercase letters. Determine the minimum number of columns that can be removed to ensure that each row is ordered from top to bottom lexicographically. That is, the letter at each column is lexicographically later as you go down each row. It does not matter whether each row itself is ordered lexicographically.
For example, given the following table:
cba
daf
ghi
This is not ordered because of the a in the center. We can remove the second column to make it ordered:
ca
df
gi
So your function should return 1, since we only needed to remove 1 column.
As another example, given the following table:
abcdef
Your function should return 0, since the rows are already ordered (there's only one row).
As another example, given the following table:
zyx
wvu
tsr
Your function should return 3, since we would need to remove all the columns to order it. Solution
This problem was asked recently by Google.
Given k sorted singly linked lists, write a function to merge all the lists into one sorted singly linked list. Solution
This problem was asked by Facebook.
Given an array of integers, write a function to determine whether the array could become non-decreasing by modifying at most 1 element.
For example, given the array [10, 5, 7], you should return true, since we can modify the 10 into a 1 to make the array non-decreasing.
Given the array [10, 5, 1], you should return false, since we can't modify any one element to get a non-decreasing array.
This problem was asked by Google.
Given the root of a binary tree, return a deepest node. For example, in the following tree, return d.
a
/ \
b c
/
d
This problem was asked by Google.
Invert a binary tree.
For example, given the following tree:
a
/ \
b c
/ \ /
d e f
should become:
a
/ \
c b
\ / \
f e d
This problem was asked by Google.
Given a string of parentheses, write a function to compute the minimum number of parentheses to be removed to make the string valid (i.e. each open parenthesis is eventually closed).
For example, given the string "()())()", you should return 1. Given the string ")(", you should return 2, since we must remove all of them.
This problem was asked by Uber.
A rule looks like this:
A NE B
This means this means point A is located northeast of point B.
A SW C
means that point A is southwest of C.
Given a list of rules, check if the sum of the rules validate. For example:
A N B B NE C C N A does not validate, since A cannot be both north and south of C.
A NW B A N B is considered valid.
This problem was asked by Airbnb.
We're given a hashmap with a key courseId and value a list of courseIds, which represents that the prerequsite of courseId is courseIds. Return a sorted ordering of courses such that we can finish all courses.
Return null if there is no such ordering.
For example, given {'CSC300': ['CSC100', 'CSC200'], 'CSC200': ['CSC100'], 'CSC100': []}, should return ['CSC100', 'CSC200', 'CSCS300'].
This problem was asked by Google.
Given a binary tree of integers, find the maximum path sum between two nodes. The path must go through at least one node, and does not need to go through the root.
This problem was asked by Palantir.
Given a number represented by a list of digits, find the next greater permutation of a number, in terms of lexicographic ordering. If there is not greater permutation possible, return the permutation with the lowest value/ordering.
For example, the list [1,2,3] should return [1,3,2]. The list [1,3,2] should return [2,1,3]. The list [3,2,1] should return [1,2,3].
Can you perform the operation without allocating extra memory (disregarding the input memory)?
This problem was asked by Microsoft.
Given a number in the form of a list of digits, return all possible permutations.
For example, given [1,2,3], return [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]. Solution
This problem was asked by Google.
Given a word W and a string S, find all starting indices in S which are anagrams of W.
For example, given that W is "ab", and S is "abxaba", return 0, 3, and 4.
This problem was asked by Google.
Given the root of a binary search tree, and a target K, return two nodes in the tree whose sum equals K.
For example, given the following tree and K of 20
10
/ \
5 15
/ \
11 15
Return the nodes 5 and 15.
Given a real number n, find the square root of n. For example, given n = 9, return 3.
Given an array of numbers representing the stock prices of a company in chronological order and an integer k, return the maximum profit you can make from k buys and sells. You must buy the stock before you can sell it, and you must sell the stock before you can buy it again.
For example, given k = 2 and the array [5, 2, 4, 0, 1], you should return 3.
Given the head to a singly linked list, where each node also has a “random” pointer that points to anywhere in the linked list, deep clone the list.
This problem was asked by Amazon.
Given a node in a binary search tree, return the next bigger element, also known as the inorder successor.
For example, the inorder successor of 22 is 30.
10
/ \
5 30
/ \
22 35
You can assume each node has a parent pointer.
Implement a bit array.
A bit array is a space efficient array that holds a value of 1 or 0 at each index.
init(size): initialize the array with size set(i, val): updates index at i with val where val is either 1 or 0. get(i): gets the value at index i.
This problem was asked by Google.
Find the minimum number of coins required to make n cents.
You can use standard American denominations, that is, 1¢, 5¢, 10¢, and 25¢.
For example, given n = 16, return 3 since we can make it with a 10¢, a 5¢, and a 1¢.
This problem was asked by Google.
Given an iterator with methods next() and hasNext(), create a wrapper iterator, PeekableInterface, which also implements peek(). peek shows the next element that would be returned on next().
Here is the interface:
class PeekableInterface(object):
def __init__(self, iterator):
pass
def peek(self):
pass
def next(self):
pass
def hasNext(self):
passThis problem was asked by Google.
Given the head of a singly linked list, swap every two nodes and return its head.
For example, given 1 -> 2 -> 3 -> 4, return 2 -> 1 -> 4 -> 3.
This question was asked by BufferBox.
Given a binary tree where all nodes are either 0 or 1, prune the tree so that subtrees containing all 0s are removed.
For example, given the following tree:
0
/ \
1 0
/ \
1 0
/ \
0 0
should be pruned to:
0
/ \
1 0
/
1
We do not remove the tree at the root or its left child because it still has a 1 as a descendant. Solution
This problem was asked by Goldman Sachs.
Given a list of numbers L, implement a method sum(i, j) which returns the sum from the sublist L[i:j] (including i, excluding j).
For example, given L = [1, 2, 3, 4, 5], sum(1, 3) should return sum([2, 3]), which is 5.
You can assume that you can do some pre-processing. sum() should be optimized over the pre-processing step.
This problem was asked by LinkedIn.
Given a list of points, a central point, and an integer k, find the nearest k points from the central point.
For example, given the list of points [(0, 0), (5, 4), (3, 1)], the central point (1, 2), and k = 2, return [(0, 0), (3, 1)].
This problem was asked by MongoDB.
Given a list of elements, find the majority element, which appears more than half the time (> floor(len(lst) / 2.0)).
You can assume that such element exists.
For example, given [1, 2, 1, 1, 3, 4, 0], return 1.
This problem was asked by Jane Street.
Given an arithmetic expression in Reverse Polish Notation, write a program to evaluate it.
The expression is given as a list of numbers and operands. For example: [5, 3, '+'] should return 5 + 3 = 8.
For example, [15, 7, 1, 1, '+', '-', '/', 3, '*', 2, 1, 1, '+', '+', '-'] should return 5, since it is equivalent to ((15 / (7 - (1 + 1))) * 3) - (2 + (1 + 1)) = 5.
You can assume the given expression is always valid.
This problem was asked by Facebook.
Given an N by N matrix, rotate it by 90 degrees clockwise.
For example, given the following matrix:
[[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
you should return:
[[7, 4, 1],
[8, 5, 2],
[9, 6, 3]]
Follow-up: What if you couldn't use any extra space?
Given a start word, an end word, and a dictionary of valid words, find the shortest transformation sequence from start to end such that only one letter is changed at each step of the sequence, and each transformed word exists in the dictionary. If there is no possible transformation, return null. Each word in the dictionary have the same length as start and end and is lowercase.
For example, given start = "dog", end = "cat", and dictionary = {"dot", "dop", "dat", "cat"}, return ["dog", "dot", "dat", "cat"].
Given start = "dog", end = "cat", and dictionary = {"dot", "tod", "dat", "dar"}, return null as there is no possible transformation from dog to cat.
There is a string, s, of lowercase English letters that is repeated infinitely many times. Given an integer, N , find and print the number of letter a's in the first letters of the infinite string.
This problem was asked by Amazon.
You are given a list of data entries that represent entries and exits of groups of people into a building. An entry looks like this:
{"timestamp": 1526579928, count: 3, "type": "enter"}
This means 3 people entered the building. An exit looks like this:
{"timestamp": 1526580382, count: 2, "type": "exit"}
This means that 2 people exited the building. timestamp is in Unix time.
Find the busiest period in the building, that is, the time with the most people in the building. Return it as a pair of (start, end) timestamps. You can assume the building always starts off and ends up empty, i.e. with 0 people inside.
This problem was asked by Dropbox.
Given a string s and a list of words words, where each word is the same length, find all starting indices of substrings in s that is a concatenation of every word in words exactly once.
For example, given s = "dogcatcatcodecatdog" and words = ["cat", "dog"], return [0, 13], since "dogcat" starts at index 0 and "catdog" starts at index 13.
Given s = "barfoobazbitbyte" and words = ["dog", "cat"], return [] since there are no substrings composed of "dog" and "cat" in s.
The order of the indices does not matter.
Describe and give an example of each of the following types of polymorphism:
Ad-hoc polymorphism Parametric polymorphism Subtype polymorphism
- Ad-hoc polymorphism
- Allow multiple functions that perform an operation on different
- add(int, int) and add(str, str) would be separately implemented
- Parametric polymorphism
- This allows a function to deal with generics, and therefore on any concrete definition of the generic.
- e.g. A List type in Java, regardless of which objects are in the list
- Subtype polymorphism
- This allows subclass instances to be treated by a function they same way as it would superclass instances
- e.g. Instances of Cat will be operated on a function the same way as instances of it's superclass Animal.
Determine whether there exists a one-to-one character mapping from one string s1 to another s2.
For example, given s1 = abc and s2 = bcd, return true since we can map a to b, b to c, and c to d.
Given s1 = foo and s2 = bar, return false since the o cannot map to two characters.
This problem was asked by Airbnb.
Given a linked list and a positive integer k, rotate the list to the right by k places.
For example, given the linked list 7 -> 7 -> 3 -> 5 and k = 2, it should become 3 -> 5 -> 7 -> 7.
Given the linked list 1 -> 2 -> 3 -> 4 -> 5 and k = 3, it should become 3 -> 4 -> 5 -> 1 -> 2.
This problem was asked by Square.
A competitive runner would like to create a route that starts and ends at his house, with the condition that the route goes entirely uphill at first, and then entirely downhill.
Given a dictionary of places of the form {location: elevation}, and a dictionary mapping paths between some of these locations to their corresponding distances, find the length of the shortest route satisfying the condition above. Assume the runner's home is location 0.
For example, suppose you are given the following input:
elevations = {0: 5, 1: 25, 2: 15, 3: 20, 4: 10}
paths = {
(0, 1): 10,
(0, 2): 8,
(0, 3): 15,
(1, 3): 12,
(2, 4): 10,
(3, 4): 5,
(3, 0): 17,
(4, 0): 10
}
In this case, the shortest valid path would be 0 -> 2 -> 4 -> 0, with a distance of 28. Solution
Google Interview Question
You have access to ranked lists of songs for various users. Each song is represented as an integer, and more preferred songs appear earlier in each list. For example, the list [4, 1, 7] indicates that a user likes song 4 the best, followed by songs 1 and 7. Given a set of these ranked lists, interleave them to create a playlist that satisfies everyone's priorities. For example, suppose your input is {[1, 7, 3], [2, 1, 6, 7, 9], [3, 9, 5]}. In this case a satisfactory playlist could be [2, 1, 6, 7, 3, 9, 5].
https://wgallagher86.medium.com/hex-to-base64-encoding-in-go-ee7fd8e8fd69 This problem was asked by Paypal.
Read this Wikipedia article on Base64 encoding.
Implement a function that converts a hex string to base64.
For example, the string:
deadbeef
should produce:
3q2+7w==
This problem was asked by Apple.
You are given a hexadecimal-encoded string that has been XOR'd against a single char.
Decrypt the message. For example, given the string:
7a575e5e5d12455d405e561254405d5f1276535b5e4b12715d565b5c551262405d505e575f
You should be able to decrypt it and get:
Hello world from Daily Coding Problem
This problem was asked by Airbnb.
Given an array of integers, return the largest range, inclusive, of integers that are all included in the array.
For example, given the array [9, 6, 1, 3, 8, 10, 12, 11], return (8, 12) since 8, 9, 10, 11, and 12 are all in the array.
This problem was asked by Goldman Sachs.
Given a list of numbers L, implement a method sum(i, j) which returns the sum from the sublist L[i:j] (including i, excluding j).
For example, given L = [1, 2, 3, 4, 5], sum(1, 3) should return sum([2, 3]), which is 5.
You can assume that you can do some pre-processing. sum() should be optimized over the pre-processing step.
This problem was asked by Snapchat.
Given an array of time intervals (start, end) for classroom lectures (possibly overlapping), find the minimum number of rooms required.
For example, given [(30, 75), (0, 50), (60, 150)], you should return 2.
This problem was asked by Google.
You are in an infinite 2D grid where you can move in any of the 8 directions:
(x,y) to
(x+1, y),
(x - 1, y),
(x, y+1),
(x, y-1),
(x-1, y-1),
(x+1,y+1),
(x-1,y+1),
(x+1,y-1)
You are given a sequence of points and the order in which you need to cover the points. Give the minimum number of steps in which you can achieve it. You start from the first point.
Example:
Input: [(0, 0), (1, 1), (1, 2)]
Output: 2
It takes 1 step to move from (0, 0) to (1, 1). It takes one more step to move from (1, 1) to (1, 2).
This question was asked by BufferBox.
Given a binary tree where all nodes are either 0 or 1, prune the tree so that subtrees containing all 0s are removed.
For example, given the following tree:
0
/ \
1 0
/ \
1 0
/ \
0 0
should be pruned to:
0
/ \
1 0
/
1
We do not remove the tree at the root or its left child because it still has a 1 as a descendant.
This problem was asked by Alibaba.
Given an even number (greater than 2), return two prime numbers whose sum will be equal to the given number.
A solution will always exist. See Goldbach’s conjecture.
Example:
Input: 4
Output: 2 + 2 = 4
If there are more than one solution possible, return the lexicographically smaller solution.
If [a, b] is one solution with a <= b, and [c, d] is another solution with c <= d, then
[a, b] < [c, d]
If a < c OR a==c AND b < d.
This problem was asked by Google.
You're given a string consisting solely of (, ), and *. * can represent either a (, ), or an empty string. Determine whether the parentheses are balanced.
For example, (()* and (*) are balanced. )*( is not balanced.
Good morning! Here's your coding interview problem for today.
This problem was asked by LinkedIn.
You are given a string consisting of the letters x and y, such as xyxxxyxyy. In addition, you have an operation called flip, which changes a single x to y or vice versa.
Determine how many times you would need to apply this operation to ensure that all x's come before all y's. In the preceding example, it suffices to flip the second and sixth characters, so you should return 2.
This problem was asked by Google.
Given a set of distinct positive integers, find the largest subset such that every pair of elements in the subset (i, j) satisfies either i % j = 0 or j % i = 0.
For example, given the set [3, 5, 10, 20, 21], you should return [5, 10, 20]. Given [1, 3, 6, 24], return [1, 3, 6, 24].
This problem was asked by Netflix.
Implement a queue using a set of fixed-length arrays.
The queue should support enqueue, dequeue, and get_size operations.