Backtracking

//C++ Program to Array Permutations
#include<bits/stdc++.h>
using namespace std;

void solve(vector<int>& nums,int index,vector<vector<int>>& ans){
    //If index is equal to size of num then store our num vector in ans and return 
        if(index>=nums.size()){
            ans.push_back(nums);
            return;
        }
        
    //Looping from index till size of the array
        for(int i=index;i<nums.size();i++){
            //Swap the ind and ith numbers in nums array
            swap(nums[index],nums[i]);
            //Recursive Call with increase in the index
            solve(nums,index+1,ans);
            //backtracking
            swap(nums[index],nums[i]);
        }
}

vector<vector<int>> arrayPermutations(vector<int>& nums) {
    //Initializing answer vector where we store permutations
        vector<vector<int>> ans;
        int index = 0;   //ind of the starting point
    
        //Function Call 
        solve(nums,index,ans);
    
        return ans;
}

int main() {
    //Inititalizing array
    vector<int> arr = {1,2,3,4};
    
    //Function Call
    vector<vector<int>> permutations = arrayPermutations(arr);
    //Printing the permutations of vector arr
    cout<<"Permutations of {1,2,3,4} are : "<<endl;
    for(int i=0;i<permutations.size();i++){
        cout<<" [ ";
        for(int j=0;j<permutations[i].size();j++){
            cout<<permutations[i][j]<<" ";
        }
        if(i!=permutations.size()-1) cout<<"] ,";
    }
    cout<<"]";
    return 0;
}