JS实现经典的排序算法

几大经典排序算法实现： 1.排序算法介绍：

2.基本算法 2.1 冒泡排序

function bubbleSort(arr) {
  var len = arr.length
  for (var i = 0; i < len; i++) {
    for (var j = 0; j < len - 1 - i; j++) {
      if (arr[j] > arr[j + 1]) {
        ;[arr[j], arr[j + 1]] = [arr[j + 1], arr[j]]
      }
    }
  }
  return arr
}

2.2 选择排序

function selectionSort(arr) {
  for (let i = 0; i < arr.length; i++) {
    let min = i
    for (let j = i + 1; j < arr.length; j++) {
      if (arr[j] < arr[min]) {
        min = j
      }
    }
    ;[arr[i], arr[min]] = [arr[min], arr[i]]
  }
  return arr
}

2.3 插入排序

function insertionSort(arr) {
  for (let i = 1; i < arr.length; i++) {
    let preIndex = i - 1
    let current = arr[i]
    while (preIndex >= 0 && arr[preIndex] > current) {
      arr[preIndex + 1] = arr[preIndex]
      preIndex--
    }
    arr[preIndex + 1] = current
  }
  return arr
}

2.4 归并排序

function mergeSort(arr) {
  //采用自上而下的递归方法
  var len = arr.length
  if (len < 2) {
    return arr
  }
  var middle = Math.floor(len / 2),
    left = arr.slice(0, middle),
    right = arr.slice(middle)
  return merge(mergeSort(left), mergeSort(right))
}

function merge(left, right) {
  var result = []

  while (left.length && right.length) {
    if (left[0] <= right[0]) {
      result.push(left.shift())
    } else {
      result.push(right.shift())
    }
  }

  while (left.length) result.push(left.shift())

  while (right.length) result.push(right.shift())

  return result
}

2.5 快速排序

function quickSort(arr) {
  if (arr.length <= 1) return arr
  let midIndex = Math.floor(arr.length / 2)
  let mid = arr.splice(midIndex, 1)[0] //找出基准元素
  let left = []
  let right = []
  for (let i of arr) {
    if (i > mid) {
      right.push(i)
    } else {
      left.push(i)
    }
  }
  return [...quickSort(left), mid, ...quickSort(right)]
}

参考链接：十大经典算法排序总结对比