五种排序算法

冒泡排序

const bubbleSort = (arr) => {
 for (let i = 0; i < arr.length; i++) {
  for (let j = i; j < arr.length; j++) {
    if (arr[j] < arr[i]) {
     let cur = arr[j]
     arr[j] = arr[i]
     arr[i] = cur
    }
  }
 }
 return arr
}

快速排序

const quickSort = (arr) => {
 if (arr.length < 2) return arr
 let mid = Math.floor(arr.length / 2)
 let midVal = arr.splice(mid, 1)[0]
 let left = []
 let right = []
 for (let i = 0; i < arr.length; i++) {
  if (arr[i] < midVal) {
   left.push(arr[i])
  } else {
   right.push(arr[i])
  }
 }
 return quickSort(left).concat([midVal], quickSort(right))
}

选择排序

const selectSort = (arr) => {
 let min
 let item
 for (let i = 0; i < arr.length; i++) {
  min = i
  for (let j = i; j < arr.length; j++) {
   if (arr[j] < arr[min]) min = j
  }
  item = arr[min]
  arr[min] = arr[i]
  arr[i] = item
 }
 return arr
}

插入排序

const insertSort = (arr) => {
 let index
 let indexVal
 for (let i = 1; i < arr.length; i++) {
  index = i
  indexVal = arr[i]
  while (index > 0 && arr[index - 1] > indexVal) {
   arr[index] = arr[index - 1]
   index--
  }
  arr[index] = indexVal
 }
 return arr
}

归并排序

function mergeSort (arr) {
 if (arr.length < 2) return arr
 let mid = Math.floor(arr.length / 2)
 let left = arr.slice(0, mid)
 let right = arr.slice(mid)
 return merge(mergeSort(left), mergeSort(right))
}

function merge (left, right) {
 let newArr = []
 while (left.length > 0 && right.length > 0) {
  if (left[0] < right[0]) {
   newArr.push(left.shift())
  } else {
   newArr.push(right.shift())
  }
 }
 while(left.length) {
  newArr.push(left.shift())
 }
 while(right.length) {
  newArr.push(right.shift())
 }
 return newArr
}