https://leetcode.com/problems/n-queens/

nQueen.cpp

void placeQueen(vector<int>& colNo, vector<bool>& usedCol, vector<bool>& rowPlusCol, vector<bool>& rowMinusCol, int row, vector<vector<string>>& result)
{
    int n = usedCol.size();
    
    if (row == n)
    {
        //all queens have been placed
        vector<string> board(n, string(n, '.'));
        int i;
        for (i = 0; i < n; ++i)
            board[i][colNo[i]] = 'Q';
        
        result.push_back(board);
        return;
    }
    
    int c;
    for (c = 0; c < n; ++c)
    {
        if (!usedCol[c] && !rowPlusCol[row+c] && !rowMinusCol[row-c + n-1])
        {
            usedCol[c] = true;
            rowPlusCol[row+c] = true;
            rowMinusCol[row-c + n-1] = true;
            
            colNo[row] = c;
            placeQueen(colNo, usedCol, rowPlusCol, rowMinusCol, row+1, result);
            colNo[row] = -1;
            
            rowMinusCol[row-c + n-1] = false;
            rowPlusCol[row+c] = false;
            usedCol[c] = false;
        }
    }
}

class Solution {
public:
    vector<vector<string>> solveNQueens(int n) {
        vector<int> colNo(n, -1);
        vector<bool> usedCol(n, false);
        vector<bool> rowPlusCol(2*n, false), rowMinusCol(2*n, false);
        
        vector<vector<string>> result;
        
        placeQueen(colNo, usedCol, rowPlusCol, rowMinusCol, 0, result);
        return result;
    }
};