leetCode 30天

题太难了，就来一个N皇后吧
51. N 皇后

class Solution {
private:vector<vector<string>> res;void backtracking(int n, int row, vector<string>& chessboard){if (row == n){res.push_back(chessboard);return;}for (int col = 0; col<n; col++){if (isValid(row, col, chessboard, n)){chessboard[row][col] = 'Q';backtracking(n, row+1,chessboard);chessboard[row][col] = '.';}}}bool isValid(int row, int col, vector<string>& chessboard, int n){// 检查列for (int i = 0; i<row; i++){if (chessboard[i][col] == 'Q'){return false;}}// 检查45度角for (int i = row-1,j = col-1; i>=0 && j>=0; i--,j--){if (chessboard[i][j] == 'Q'){return false;}}// 检查135度for (int i = row-1,j = col+1; i>=0 && j<n; i--,j++){if (chessboard[i][j] == 'Q'){return false;}}return true;}public:vector<vector<string>> solveNQueens(int n) {res.clear();vector<string> chessboard(n, string(n,'.'));backtracking(n, 0, chessboard);return res;}
};