Given a collection of distinct integers, return all possible permutations.
    Example:
    Input: [1,2,3]
    Output:
    [
    [1,2,3],
    [1,3,2],
    [2,1,3],
    [2,3,1],
    [3,1,2],
    [3,2,1]
    ]

    1. /**
    2.  * @param {number[]} nums
    3.  * @return {number[][]}
    4.  */
    5. var permute = function(nums) {
    6.     const result = [];
    7.     const size = nums.length;
    8.     const permutations = function (current = [], remaining = []) {
    9.         if (current.length >= size) {
    10.             result.push(current.slice());
    11.         }
    12.         for (let i = 0; i < remaining.length; i++) {
    13.             current.push(remaining[i]);
    14.             permutations(current.slice(), remaining.slice(0, i).concat(remaining.slice(i + 1)));
    15.             current.pop();
    16.         }
    17.     }
    18.     permutations([], nums);
    19.     return result;
    20. };

    Runtime: 68 ms, faster than 99.84% of JavaScript online submissions forPermutations.
    Memory Usage: 37.4 MB, less than 24.41% of JavaScript online submissions forPermutations.