51. N-Queens ( Leetcode )

class Solution {
public:
    bool isSafe(int size, int row, int col,  vector<string> testBoard)
    {
        int tempCol = col;
        int tempRow = row;

        while(row >= 0 && col >= 0)
        {
            if(testBoard[row][col] == 'Q') return false;
            row--;
            col--;
        }

        col = tempCol;
        row = tempRow;

        while( col >= 0)
        {
            if(testBoard[row][col] == 'Q') return false;
            col--;
        }

        col = tempCol;
        row = tempRow;

        while(row < size && col >= 0)
        {
            if(testBoard[row][col] == 'Q') return false;
            row++;
            col--;
        }

        return true;
    }

    void helper(vector<vector<string>> &chessBoard, vector<string> &testBoard, int col, int size)
    {   
        if(col == size)
        {
            chessBoard.push_back(testBoard);
            return;
        }

        // doing simple backtracking
        for(int i = 0; i < size; i++)
        {
            if(isSafe(size, i, col, testBoard))
            {
                testBoard[i][col] = 'Q';
                helper(chessBoard, testBoard, col+1, size);
                testBoard[i][col] = '.';
            }
        }
    }

    vector<vector<string>> solveNQueens(int n) 
    {
        vector<vector<string>> chessBoard;
        
        // doing this to make the board according to the 
        // given questions requirment
        vector<string> testBoard(n);
        string s(n, '.');
        for(int i = 0; i < n; i++) testBoard[i] = s;
        
        int col = 0;
        helper(chessBoard, testBoard, col, n);
        
        return chessBoard;
    }
};