Permutations

#include <bits/stdc++.h>
using namespace std;

void solve(vector<int> nums, vector<vector<int>> &ans, int i)
{
    if (i >= nums.size())
    {
        ans.push_back(nums);
        return;
    }
    for (int j = i; j < nums.size(); ++j)
    {
        swap(nums[i], nums[j]);
        solve(nums, ans, i + 1);
        // backtrack
        swap(nums[i], nums[j]);
    }
}

vector<vector<int>> permute(vector<int> &nums)
{
    vector<vector<int>> ans;
    solve(nums, ans, 0);
    return ans;
}

int main()
{
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i++)
        cin >> a[i];
    vector<vector<int>> ans = permute(a);
    for (auto i : ans)
    {
        for (auto j : i)
        {
            cout << j << " ";
        }
        cout << endl;
    }

    return 0;
}