eightQueens.cpp

#include <iostream>
#include <vector>

using namespace std; 

class Solution{
public:
	vector<vector<int> > placeQueens(int n) {
        vector<vector<int> > res;
        vector<int> pos(n, -1);
        placeQueensDFS(pos, 0, res); 
        printBoard(res); 
        return res;
    }
	void placeQueensDFS(vector<int> &pos, int row, vector<vector<int>> &res ) 
	{
		int n = pos.size(); 
		if (row == n) res.push_back(pos); 
		else {
			for (int col = 0; col < n; ++ col ){
				if (isValid(pos, row, col)) {
					pos[row] = col; 
					placeQueensDFS(pos, row + 1, res); 
					pos[row] = -1; 
				}
			}
		}
	}

	bool isValid(vector<int> &pos, int row, int col) {
		for(int i = 0; i < row; ++i) {
			if (col == pos[i] || abs(row - i) == abs(col - pos[i])) {
				return false; 
			}
		}
		return true; 
	}
	void printBoard(const vector<vector<int>> board) {
		vector<vector<int>>::const_iterator row; 
		vector<int>::const_iterator col; 
		for (row = board.begin(); row != board.end(); row++) 
			for(col = row -> begin(); col != row -> end(); col++)
				cout << *col << ""; 

			cout << endl; 
	}

};



int main() {

	Solution sol; 
	sol.placeQueens(3); 

}