1. let results = [];var permute = function(nums) {
    2.     results = [];
    3.     backtrack(nums, []);
    4.     return results;
    5. };
    6. function backtrack(nums, track) {
    7.     if (nums.length === track.length) {
    8.         results.push(track.slice());
    9.         return;
    10.     }
    11.     for (let i = 0; i < nums.length; i++) {
    12.         if (track.includes(nums[i])) continue;
    13.         track.push(nums[i]);
    14.         backtrack(nums, track);
    15.         track.pop();
    16.     }
    17. }