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46. Permutations

Medium

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.

Solution

using System.Collections.Generic;

public class Solution {
    public IList<IList<int>> Permute(int[] nums) {
        if (nums == null || nums.Length == 0) {
            return new List<IList<int>>();
        }
        IList<IList<int>> finalResult = new List<IList<int>>();
        PermuteRecur(nums, finalResult, new List<int>(), new bool[nums.Length]);
        return finalResult;
    }

    private void PermuteRecur(
            int[] nums, IList<IList<int>> finalResult, List<int> currResult, bool[] used) {
        if (currResult.Count == nums.Length) {
            finalResult.Add(new List<int>(currResult));
            return;
        }
        for (int i = 0; i < nums.Length; i++) {
            if (used[i]) {
                continue;
            }
            currResult.Add(nums[i]);
            used[i] = true;
            PermuteRecur(nums, finalResult, currResult, used);
            used[i] = false;
            currResult.RemoveAt(currResult.Count - 1);
        }
    }
}

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