1、全排列
    https://leetcode-cn.com/problems/permutations/

    1. var permute = function(nums) {
    2.     const res = []
    3.     var perm = function (nums, start, end) {
    4.         if (start == end) {
    5.               //拷贝数组
    6.               //重要
    7.             res.push(nums.concat())
    8.         } else {
    9.                 for (let i = start; i <= end; i++) {
    10.                     swap(nums, start, i)
    11.                     perm(nums, start+1, end)
    12.                     swap(nums, start, i)
    13.             }
    14.         }
    16.     }
    17.     perm(nums, 0 ,nums.length - 1)
    18.     return res
    19. };
    21. var swap = function (nums, a, b) {
    22.     let c = nums[b]
    23.     nums[b] = nums[a]
    24.     nums[a] = c
    25. }

    2、数组的子集
    https://www.cnblogs.com/linx/p/7568375.html