Problem Statement

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.

Problem Link

Permutations - LeetCode

Recursion Tree

Code

class Solution {
public:
    vector<vector<int>> permute(vector<int>& nums) {
        
        int n = nums.size();
        
        vector<vector<int>> res;
        
        permuteUtil(res,nums,0,n-1);
        
        return res;
        
    }
    
    void permuteUtil(vector<vector<int>> &res,vector<int>& nums,int l,int r)
    {
        if(l==r)
            res.push_back(nums);
        
        else
        {
            for(int i=l;i<=r;i++)
            {
                swap(nums[i],nums[l]);
                
                permuteUtil(res,nums,l+1,r);
                
                swap(nums[i],nums[l]);
            }
        }
    }
};

Complexity Analysis:

Time Complexity: O(n*n!) Note that there are n! permutations and it requires O(n) time to print a permutation.