14 算法

所有的递归都能变成循环

//基础排序
let sort = (numbers) => {
  for(let i=0; i< numbers.length -1; i++){
    console.log(`----`) //这个log很精髓
    console.log(`i: ${i}`)
    let index = minIndex(numbers.slice(i))+ i
    console.log(`index: ${index}`)
    console.log(`min: ${numbers[index]}`)
    if(index!==i){
      swap(numbers, index, i)
      console.log(`swap ${index}: ${i}`)
      console.log(numbers)
    }
}
  return numbers
}
let swap = (array, i, j) => {
  let temp = array[i]
  array[i] = array[j]
  array[j] = temp
}
let minIndex = (numbers) => {
  let index = 0
  for(let i=1; i<numbers.length; i++){
    if(numbers[i] < numbers[index]){
      index = i
    }
  }
  return index
}
// 快速排序
let quickSort = arr => {
　　if (arr.length <= 1) { return arr; }
　　let pivotIndex = Math.floor(arr.length / 2);
　　let pivot = arr.splice(pivotIndex, 1)[0];
　　let left = [];
　　let right = [];
　　for (let i = 0; i < arr.length; i++){
　　　　if (arr[i] < pivot) { left.push(arr[i])
　　　　} else { right.push(arr[i]) }
　　}
　　return quickSort(left).concat(
             [pivot], quickSort(right) )
}
// 归并排序
let mergeSort = arr =>{
  let k = arr.length
  if(k===1){return arr}
  let left = arr.slice(0, Math.floor(k/2))
  let right = arr.slice(Math.floor(k/2))
  return merge(mergeSort(left), mergeSort(right))
}
let merge = (a, b) => {
  if(a.length === 0) return b
  if(b.length === 0) return a
  return a[0] > b[0] ?
     [b[0]].concat(merge(a, b.slice(1))) :
     [a[0]].concat(merge(a.slice(1), b))
}
// 计数排序
let countSort = arr =>{
  let hashTable = {}, max = 0, result = []
  for(let i=0; i<arr.length; i++){ // 遍历数组
    if(!(arr[i] in hashTable)){
      hashTable[arr[i]] = 1
    }else{
      hashTable[arr[i]] += 1
    }
    if(arr[i] > max) {max = arr[i]}
  }
  for(let j=0; j<=max; j++){ // 遍历哈希表
    if(j in hashTable){
      for(let i = 0; i<hashTable[j]; i++){
        result.push(j)
      }
    }
  }
  return result
}