题目：

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代码(首刷看解析 2024年2月6日）：

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, n, chessboard)) {chessboard[row][col] = 'Q';backtracking(n, row + 1, chessboard);chessboard[row][col] = '.';}}return;}bool isValid(int row, int col, int n, vector<string>& chessboard) {/*检查列*/for (int i = 0; i <= row; ++i) {if (chessboard[i][col] == 'Q') {return false;}}/*检查右上斜角*/for (int i = row - 1, j = col + 1; i >=0 && j < n; --i, ++j) {if(chessboard[i][j] == 'Q'){return false;}}/*检查左上斜角*/for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; --i, --j) {if(chessboard[i][j] == 'Q'){return false;}} return true;}
public:vector<vector<string>> solveNQueens(int n) {vector<string> chessboard(n, string(n, '.'));backtracking(n, 0, chessboard);return res;}
};