0046-permutations.js

/**
 * https://leetcode.com/problems/permutations/solution/
 * Time O(N!) | Space(N!)
 * @param {number[]} nums
 * @return {number[][]}
 */
var permute = function (nums) {
    return dfs(nums);
};

var dfs = function (nums, permutation = [], permutations = []) {
    const isBaseCase = nums.length === permutation.length;
    if (isBaseCase) return permutations.push(permutation.slice());

    for (let i = 0; i < nums.length; i++) {
        if (permutation.includes(nums[i])) continue;

        backTrack(nums, i, permutation, permutations);
    }

    return permutations;
};

const backTrack = (nums, i, permutation, permutations) => {
    permutation.push(nums[i]);
    dfs(nums, permutation, permutations);
    permutation.pop();
};

/**
 * https://leetcode.com/problems/permutations/solution/
 * Time O(N!) | Space(N!)
 * @param {number[]} nums
 * @return {number[][]}
 */
var permute = function (nums) {
    return bfs(nums);
};

const bfs = (nums, levels = [[]], permutations = []) => {
    for (const num of nums) {
        for (let i = levels.length - 1; 0 <= i; i--) {
            const previousLevel = levels.shift();

            for (let index = 0; index < previousLevel.length + 1; index++) {
                const level = reArrangeSet(previousLevel, num, index);

                const isBaseCase = level.length === nums.length;
                if (isBaseCase) {
                    permutations.push(level);
                    continue;
                }

                levels.push(level);
            }
        }
    }

    return permutations;
};

const reArrangeSet = (previousLevel, num, index) => {
    const [before, after] = [
        previousLevel.slice(0, index),
        previousLevel.slice(index),
    ];

    return [...before, num, ...after];
};