1、快排
https://segmentfault.com/a/1190000017814119
思路：将数组分为两边，小的一道左边，大的移到右边，后递归
注意 ：
var pivot = arr.splice(pivotIndex, 1)[0];
return quickSort(left).concat([pivot], quickSort(right));

  1. var quickSort = function(arr) {
  2.   if (arr.length <= 1) {
  3.     return arr;
  4.   } // 重要
  5.   var pivotIndex = Math.floor(arr.length / 2);
  6.   var pivot = arr.splice(pivotIndex, 1)[0];
  7.   var left = [];
  8.   var right = [];
  10.   for (var i = 0; i < arr.length; i++) {
  11.     if (arr[i] < pivot) {
  12.       left.push(arr[i]);
  13.     } else {
  14.       right.push(arr[i]);
  15.     }
  16.   }
  17.   return quickSort(left).concat([pivot], quickSort(right));
  18. };

2、冒泡
时间复杂度 o(n*n)
重点：循环
j < nums.len -1
i < nums.leng -1 -j

  1. var bubbleSort = function(nums) {
  2.     const len = nums.length - 1
  3.     for (let j = 0; j < len; j++) {
  4.         for (let i = 0; i < len -j; i++ ) {
  5.             if (nums[i] > nums[i+1]) {
  6.                 let temp = nums[i]
  7.                 nums[i] = nums[i+1]
  8.                 nums[i+1] = temp
  9.             }
  10.         }
  11.     }
  12.     return nums
  13. }

448. 找到所有数组中消失的数字

https://leetcode-cn.com/problems/find-all-numbers-disappeared-in-an-array/