N-Queens leetcode solution in c++

 

The n-queens puzzle is the problem of placing n queens on an n x n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle. You may return the answer in any order.

Each solution contains a distinct board configuration of the n-queens' placement, where 'Q' and '.' both indicate a queen and an empty space, respectively.

class Solution {

public:

vector<vector<string> > solveNQueens(int n) {

vector<vector<string> > res;

vector<string> nQueens(n, string(n, '.'));

solveNQueens(res, nQueens, 0, n);

return res;

}

private:

void solveNQueens(vector<vector<string> > &res, vector<string> &nQueens, int row, int &n) {

if (row == n) {

res.push_back(nQueens);

return;

}

for (int col = 0; col != n; ++col)

if (isValid(nQueens, row, col, n)) {

nQueens[row][col] = 'Q';

solveNQueens(res, nQueens, row + 1, n);

nQueens[row][col] = '.';

}

}

bool isValid(std::vector<std::string> &nQueens, int row, int col, int &n) {

for (int i = 0; i != row; ++i)

if (nQueens[i][col] == 'Q')

return false;

for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; --i, --j)

if (nQueens[i][j] == 'Q')

return false;

for (int i = row - 1, j = col + 1; i >= 0 && j < n; --i, ++j)

if (nQueens[i][j] == 'Q')

return false;

return true;

}

};