N-Queen

#include <iostream>
#include <vector>
#include <string>

using namespace std;

class Solution {
private:
    bool checkDiagonal(vector<pair<int, int> > qv, pair<int, int> current) {
        int length = qv.size();
        for (int i = 0; i < length; i++) {
            if (abs(qv[i].first - current.first) == abs(qv[i].second - current.second)) {
                return false;
            }
        }

        return true;
    }

    vector<string> toString(vector<pair<int, int> > qv, int n) {
        string line(n, '.');
        vector<string> string_qv(n, line);

        for (int i = 0; i < n; i++) {
            string_qv[qv[i].first][qv[i].second] = 'Q';
        }

        return string_qv;
    }

    void dfs(vector<vector<string> > &result, vector<pair<int, int> > qv, int counter, int visited[], int n) {
        if (counter == n) {
            result.push_back(toString(qv, n));
        }

        for (int i = 0; i < n; i++) {
            if (!visited[i] && checkDiagonal(qv, make_pair(counter, i))) {
                visited[i] = 1;
                qv.push_back(make_pair(counter, i));
                dfs(result, qv, counter + 1, visited, n);
                visited[i] = 0;
                qv.pop_back();
            }
        }
    }

public:
    vector<vector<string> > solveNQueens(int n) {
        vector<vector<string> > result;
        vector<pair<int, int> > qv;
        int counter = 0;
        int visited[n];
        memset(visited, 0, sizeof(int));

        dfs(result, qv, counter, visited, n);

        return result;
    }
};

int main(int argc, char const* argv[])
{
    Solution s;
    int n = 5;
    vector<vector<string> > result = s.solveNQueens(n);

    int number = result.size();
    for (int i = 0; i < number; i++) {
        for (int j = 0; j < n; j++) {
            cout << result[i][j] << endl;
        }
        cout << endl;
    }

    return 0;
}