N-Queen Problem

//{ Driver Code Starts
// Initial Template for C++

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

// } Driver Code Ends
// User function Template for C++

class Solution{
public:
    vector<vector<int>> ans;
    bool isSafe(vector<vector<int>> &board,int r,int c,int n)
    {
        for(int i=0;i<r;i++)
        {
            if(board[i][c]==1)
            {
                return false;
            }
        }
        for(int i=r-1,j=c-1;i>=0 && j>=0;i--,j--)
        {
            if(board[i][j]==1)
            {
                return false;
            }
        }
        for(int i=r-1,j=c+1;i>=0 && j<n;i--,j++)
        {
            if(board[i][j]==1)
            {
                return false;
            }
        }
        return true;
    }
    void helper(vector<vector<int>> &board,int n,int r)
    {
        if(r==n)
        {
            vector<int> temp;
            for(int i=0;i<n;i++)
            {
                for(int j=0;j<n;j++)
                {
                    if(board[i][j]==1)
                    {
                        temp.push_back(j+1);
                    }
                }
            }
            ans.push_back(temp);
            return;
        }
        for(int i=0;i<n;i++)
        {
            if(isSafe(board,r,i,n))
            {
                board[r][i]=1;
                helper(board,n,r+1);
                board[r][i]=0;
            }
        }
    }
    vector<vector<int>> nQueen(int n) {
        // code here
        vector<vector<int>> board(n,vector<int>(n,0));
        helper(board,n,0);
        return ans;
    }
};

//{ Driver Code Starts.

int main(){
    int t;
    cin>>t;
    while(t--){
        int n;
        cin>>n;

        Solution ob;
        vector<vector<int>> ans = ob.nQueen(n);
        if(ans.size() == 0)
            cout<<-1<<"\n";
        else {
            for(int i = 0;i < ans.size();i++){
                cout<<"[";
                for(int u: ans[i])
                    cout<<u<<" ";
                cout<<"] ";
            }
            cout<<endl;
        }
    }
    return 0;
}
// } Driver Code Ends