Permutations.js

// Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

// Example 1:

// Input: nums = [1,2,3]
// Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

// Example 2:

// Input: nums = [0,1]
// Output: [[0,1],[1,0]]

// Example 3:

// Input: nums = [1]
// Output: [[1]]

// Constraints:

//     1 <= nums.length <= 6
//     -10 <= nums[i] <= 10
//     All the integers of nums are unique.

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
var permute = function (nums) {
  // global result
  let result = [];

  // dfs helper function
  const dfs = (i, nums) => {
    // base case
    if (i === nums.length) {
      result.push(nums.slice());
      return;
    }

    // dfs recursive case
    for (let j = i; j < nums.length; j++) {
      [nums[i], nums[j]] = [nums[j], nums[i]];
      dfs(i + 1, nums);
      [nums[i], nums[j]] = [nums[j], nums[i]];
    }
  };
  dfs(0, nums);
  return result;
};