GFG PTOD | 30 Jan | N-Queen Problem | Hard | Backtracking

void solve(int colm, int n, vector<bool> &col, vector<bool> &ldiag, vector<bool> &rdiag, vector<vector<int>> &ans, vector<int> &res) {
        for(int i=0; i<n; i++) {
            if(colm == n) {
                ans.push_back(res);
                return;
            }
            if(!col[i] && !ldiag[colm-i + n-1] && !rdiag[i+colm]) {
                res.push_back(i+1);
                col[i] = true;
                ldiag[colm-i+n-1] = true;
                rdiag[i+colm] = true;
                solve(colm+1, n, col, ldiag, rdiag, ans, res);
                
                res.pop_back();
                col[i] = false;
                ldiag[colm-i+n-1] = false;
                rdiag[i+colm] = false;
                
            }
        }
        
    }
    vector<vector<int>> nQueen(int n) {
        // code here
        vector<bool>col(n, false);
        vector<bool>ldiag(2*n-1, false);
        vector<bool>rdiag(2*n-1, false);
        vector<vector<int>> ans;
        vector<int> res;
        solve(0, n, col, ldiag, rdiag, ans, res);
        return ans;
    }