Completed PreCourse2

Exercise_1.java

@@ -1,17 +1,34 @@
-class BinarySearch { 
+// Time Complexity : O(log n) where n is the size of the array
+// Space Complexity : O(1)
+class BinarySearch {
     // Returns index of x if it is present in arr[l.. r], else return -1 
-    int binarySearch(int arr[], int l, int r, int x) 
-    { 
+    int binarySearch(int arr[], int l, int r, int x)
+    {
         //Write your code here
-    } 
+        int mid = 0;
+        while(r >= l) {
+            //calculate middle index
+            mid = l+(r-l)/2;
+            // found the element return the index
+            if(arr[mid] == x) return mid;
+            // if target element is bigger than the middle element, search on the right half
+            if(arr[mid] < x)
+                l = mid+1;
+            // else search on the left half
+            else
+                r = mid-1;
+        }
+
+        return -1; //Element not present
+    }
 
     // Driver method to test above 
     public static void main(String args[]) 
     { 
         BinarySearch ob = new BinarySearch(); 
-        int arr[] = { 2, 3, 4, 10, 40 }; 
+        int arr[] = { 2, 3, 4, 10, 40 };
         int n = arr.length; 
-        int x = 10; 
+        int x = 10;
         int result = ob.binarySearch(arr, 0, n - 1, x); 
         if (result == -1) 
             System.out.println("Element not present"); 

Exercise_2.java

@@ -1,48 +1,80 @@
-class QuickSort 
-{ 
-    /* This function takes last element as pivot, 
-       places the pivot element at its correct 
-       position in sorted array, and places all 
-       smaller (smaller than pivot) to left of 
-       pivot and all greater elements to right 
+// Time Complexity :
+// Best/Average Case: O(n log n) where n is the size of the array
+// Worst Case: O(n^2) , when pivot is always the smallest or largest element)
+
+// Space Complexity: O(log n) , due to recursion call
+class QuickSort
+{
+    /* This function takes last element as pivot,
+       places the pivot element at its correct
+       position in sorted array, and places all
+       smaller (smaller than pivot) to left of
+       pivot and all greater elements to right
        of pivot */
     void swap(int arr[],int i,int j){
-        //Your code here   
+        //Your code here
+        int temp = arr[i];
+        arr[i] = arr[j];
+        arr[j] = temp;
     }
-
-    int partition(int arr[], int low, int high) 
-    { 
-   	//Write code here for Partition and Swap 
-    } 
-    /* The main function that implements QuickSort() 
-      arr[] --> Array to be sorted, 
-      low  --> Starting index, 
+
+    int partition(int arr[], int low, int high)
+    {
+   	//Write code here for Partition and Swap
+        int pivot = arr[high];
+        int i = low - 1;
+
+        for(int j = i+1 ;j < high; j++) {
+            //if element is smaller or equal to pivot, swap
+            if(arr[j] <= pivot) {
+                swap(arr, ++i, j);
+            }
+        }
+        // final swap with the pivot
+        swap(arr, i+1, high);
+
+        // returns partition index
+        return i+1;
+
+    }
+    /* The main function that implements QuickSort()
+      arr[] --> Array to be sorted,
+      low  --> Starting index,
       high  --> Ending index */
-    void sort(int arr[], int low, int high) 
-    {  
-            // Recursively sort elements before 
-            // partition and after partition 
-    } 
-
+
+    void sort(int arr[], int low, int high)
+    {
+            // Recursively sort elements before
+            // partition and after partition
+        if(low < high){
+            int partIndex = partition(arr, low, high);
+
+            sort(arr, low , partIndex-1);
+            sort(arr, partIndex+1 ,high );
+        }
+
+    }
+
+
     /* A utility function to print array of size n */
-    static void printArray(int arr[]) 
-    { 
-        int n = arr.length; 
-        for (int i=0; i<n; ++i) 
-            System.out.print(arr[i]+" "); 
-        System.out.println(); 
-    } 
-  
-    // Driver program 
-    public static void main(String args[]) 
-    { 
-        int arr[] = {10, 7, 8, 9, 1, 5}; 
-        int n = arr.length; 
-  
-        QuickSort ob = new QuickSort(); 
-        ob.sort(arr, 0, n-1); 
-  
-        System.out.println("sorted array"); 
-        printArray(arr); 
-    } 
-} 
+    static void printArray(int arr[])
+    {
+        int n = arr.length;
+        for (int i=0; i<n; ++i)
+            System.out.print(arr[i]+" ");
+        System.out.println();
+    }
+
+    // Driver program
+    public static void main(String args[])
+    {
+        int arr[] = {10, 7, 8, 9, 1, 5};
+        int n = arr.length;
+
+        QuickSort ob = new QuickSort();
+        ob.sort(arr, 0, n-1);
+
+        System.out.println("sorted array");
+        printArray(arr);
+    }
+}

Exercise_3.java

@@ -1,53 +1,63 @@
-class LinkedList 
-{ 
-    Node head; // head of linked list 
-
+// Time Complexity : O(n) , where n is the size of the linked list
+// Space Complexity: O(1)
+class LinkedList
+{
+    Node head; // head of linked list
+
     /* Linked list node */
-    class Node 
-    { 
-        int data; 
-        Node next; 
-        Node(int d) 
-        { 
-            data = d; 
-            next = null; 
-        } 
-    } 
-  
+    class Node
+    {
+        int data;
+        Node next;
+        Node(int d)
+        {
+            data = d;
+            next = null;
+        }
+    }
+
     /* Function to print middle of linked list */
    //Complete this function
-    void printMiddle() 
-    { 
+    void printMiddle()
+    {
         //Write your code here
 	//Implement using Fast and slow pointers
-    } 
-
-    public void push(int new_data) 
-    { 
-        Node new_node = new Node(new_data); 
-        new_node.next = head; 
-        head = new_node; 
-    } 
+        Node slow = head;
+        Node fast = head;
+        while(fast != null && fast.next != null){
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+        System.out.println("Middle Node: " + slow.data);
+    }
+
+
+    public void push(int new_data)
+    {
+        Node new_node = new Node(new_data);
+        new_node.next = head;
+        head = new_node;
+    }
+
+    public void printList()
+    {
+        Node tnode = head;
+        while (tnode != null)
+        {
+            System.out.print(tnode.data+"->");
+            tnode = tnode.next;
+        }
+        System.out.println("NULL");
+    }
 
-    public void printList() 
-    { 
-        Node tnode = head; 
-        while (tnode != null) 
-        { 
-            System.out.print(tnode.data+"->"); 
-            tnode = tnode.next; 
-        } 
-        System.out.println("NULL"); 
-    } 
-
-    public static void main(String [] args) 
-    { 
-        LinkedList llist = new LinkedList(); 
-        for (int i=15; i>0; --i) 
-        { 
-            llist.push(i); 
-            llist.printList(); 
-            llist.printMiddle(); 
-        } 
-    } 
-} 
+    public static void main(String [] args)
+    {
+        LinkedList llist = new LinkedList();
+        for (int i=15; i>0; --i)
+        {
+            llist.push(i);
+            llist.printList();
+            llist.printMiddle();
+        }
+    }
+}