addRemote

[keep-run]

题目内容

掘金看到一个比较有意思的题目(https://juejin.cn/post/6987529814324281380#heading-11) 。大致的意思就是，需要调用接口计算两个数相加。实现一个函数实现任意个数的数字和。

实现思路

• 遍历，老老实实的计算。实现方法：
  • for遍历；
  • 递归；
  • reduce遍历；
• 基于promise.all，串行遍历变为并行;
• 做本地缓存，避免重复请求(连续执行时，后续可以秒返回)

源代码

// 第一种，普通遍历，串行执行，效率比较低
async function addFn1(args) {
  let res = 0
  for (const item of args) {
    res = await addRemote(res, item)
  }
  return res
}

// 递归实现, 串行执行， 和addFn1差距不大
async function addFn2(args = []) {
  if (args.length < 2) {
    return args[0] || 0
  }
  args.push(await addRemote(args.shift(), args.shift()))
  return addFn2(args)
}

// 基于reduce来实现
async function addFn3(args = []) {
  return args.reduce((calculator, current) => {
    return calculator.then(cal => addRemote(cal, current))
  }, Promise.resolve(0))
}

// 利用promiseAll 两两一组执行
async function addFn4(args = []) {
  let promiseChain = []
  if (args.length % 2) {
    promiseChain.push(Promise.resolve(args.shift()))
  }
  for (let i = 0; i < args.length / 2; i++) {
    promiseChain.push(addRemote(args[2 * i], args[(2 * i) + 1]))
  }
  return Promise.all(promiseChain).then(res => {
    if (res.length === 1) {
      return res[0]
    }
    return addFn4(res)
  })
}

let cache = {}
async function addFn5(args = []) {
  async function addWithCache(params) {
    let promiseChain = []
    if (params.length % 2) {
      promiseChain.push(Promise.resolve(params.shift()))
    }
    for (let i = 0; i < params.length / 2; i++) {
      let key1 = params[2 * i];
      let key2 = params[(2 * i) + 1];
      let cacheRes = cache[`${key1}${key2}`] || cache[`${key2}${key1}`]

      if (cacheRes) {
        promiseChain.push(cacheRes)
      } else {
        promiseChain.push(addRemote(key1, key2).then(res => {
          cache[`${key1}${key2}`] = res;
          return res
        }))
      }
    }
    return Promise.all(promiseChain).then(res => {
      if (res.length === 1) {
        return res[0]
      }
      return addWithCache(res)
    })
  }
  return addWithCache(args)
}

测试

const addRemote = async (a, b) => new Promise(resolve => {
  setTimeout(() => resolve(a + b), 500)
});
async function add(...inputs) {
  console.log('---------------------分割线---Fn1------------------------------')
  console.time('addFn1')
  console.log(await addFn1([...inputs]))
  console.timeEnd('addFn1')
  console.log('---------------------分割线---Fn2------------------------------')
  console.time('addFn2')
  console.log(await addFn2([...inputs]))
  console.timeEnd('addFn2')
  console.log('---------------------分割线---Fn3------------------------------')
  console.time('addFn3')
  console.log(await addFn3([...inputs]))
  console.timeEnd('addFn3')
  console.log('---------------------分割线---Fn4------------------------------')
  console.time('addFn4')
  console.log(await addFn4([...inputs]))
  console.timeEnd('addFn4')
  console.log('---------------------分割线---Fn5------------------------------')
  console.time('addFn5')
  console.log(await addFn5([...inputs]))
  console.timeEnd('addFn5')
  console.log('---------------------分割线---Fn5withcache---------------------')
  console.time('addFn5--again')
  console.log(await addFn5([...inputs]))
  console.timeEnd('addFn5--again')
}

add(1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5, 5, 6, 6, 6, 6, 6, 6, 10, 10, 10, 10)

时间统计结果