Permutations of Array

/*Given an array of integers, return all the premutations possible.
Sample Input 1:
2
3
1 2 3 
1
1
Sample Output 1:
1 2 3   1 3 2   2 1 3  2 3 1  3 1 2   3 2 1
1
*/

Approach:
we provide every element each position and take care of rest elements further recursively. or in simple mathematical terms. 
fix pisition of a number at a position and make all possible arrangements of rest of the elments. 
To Save space complexity and to make it runtime optimized, we would use backtracking to use same input array and reset the state of vector after swap again.

#include <bits/stdc++.h> 
void help(vector<int>&vec,int n,int curIn,vector<vector<int>>&ans){
    if(curIn==n-1){
        ans.push_back(vec);
        return;
    }
    for(int i=curIn;i<n;++i){
        swap(vec[i],vec[curIn]);
        help(vec,n,curIn+1,ans);
        swap(vec[i],vec[curIn]);
    }
}
vector<vector<int>> permutations(vector<int>&vec, int size) {
    vector<vector<int>>ans;
    help(vec,size,0,ans);
    return ans;
}

// T.C. : O(N!)
// S.C. : O(recursive call stack or O(N!))