【DFS】LeetCode 51. N-Queens

LeetCode 51. N-Queens

Solution1：我的答案
回溯法

class Solution {
public:
    vector<vector<string>> solveNQueens(int n) {
        vector<vector<string> > res;
        vector<int> temp;
        my_count(res, temp, n);
        return res;
    }

    void my_count(vector<vector<string> >& res, vector<int> temp, int n) { //temp临时答案，num总次数，n棋盘大小
        if (temp.size() == n) {
            my_push(res, temp, n);
            return;
        } else {
            for (int i = 0; i < n; i++) {
                temp.push_back(i);
                if (isValid(temp)) 
                    my_count(res, temp, n);
                temp.pop_back();
            }
        }
    }

    bool isValid(vector<int>& temp) {
        if (temp.size() == 1) return true;
        else {
            int k = temp.size();
            for (int i = 0; i < temp.size() - 1; i++) {
                if(temp[i] == temp[k - 1] || abs(i - k + 1) == abs(temp[i] - temp[k - 1]))
                    return false;
            }
            return true;
        }
    }

    void my_push(vector<vector<string> >& res, vector<int>& temp, int n) {
        string point = "";
        for (int i = 0; i < n; i++) point = point + ".";
        vector<string> temp_str(n, point);
        for (int i = 0; i < n; i++)
            temp_str[i].replace(temp[i], 1, "Q");
        res.push_back(temp_str);
    }
};