leetcode刷题

n皇后问题

终于到了n皇后问题，久仰大名，终于第一次解决了，其实也没有那么难

vector<vector<string>> result;
    bool isvalid(vector<string> &path, int row, int col){
        for(int i = row; i >= 0; i--){
            if(path[i][col] == 'Q'){
                return false;
            }
        }
        for(int i = row , j = col; i >= 0 && j < path.size(); i--, j++){
            if(path[i][j] == 'Q')
                return false;
        }
        for(int i = row,  j = col; i >= 0 && j >= 0; i--, j-- ){
            if(path[i][j] == 'Q')
                return false;
        }
        return true;
    }

    void backing(int n, int row, vector<string> &path){
        if(row == n){
            result.push_back(path);
            return;
        }
        
        for(int i = 0; i < n; i++){
            if(isvalid(path, row, i)){
                path[row][i] = 'Q';
                backing(n, row + 1, path);
                path[row][i] = '.';
            }
        }
    }

    vector<vector<string>> solveNQueens(int n) {
        vector<string> path(n, string(n, '.'));
        backing(n, 0, path);
        return result;
    }