八皇后问题的延伸版，回溯实现。
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class Solution { public: bool checkQueen(int** mat, int N, int r, int c) { for (int row = 0; row < N; row++) { if (row == r) continue; if (mat[row][c] == 1) return false; } // int row = r-1, col = c-1; while (row >= 0 && col >= 0) { if (mat[row][col] == 1) return false; row--; col--; } row = r + 1, col = c + 1; while (row < N && col < N) { if (mat[row][col] == 1) return false; row++; col++; } // // row = r - 1, col = c + 1; while (row >= 0 && col < N) { if (mat[row][col] == 1) return false; row--; col++; } row = r + 1, col = c - 1; while (row < N && col >= 0) { if (mat[row][col] == 1) return false; row++; col--; } // return true; } void nQueensSub(int** mat, int N, int row, int col, vector<vector<string>>& results) { if (row == N) { //print vector<string> result; for (int i = 0; i < N; i++) { string row; for (int j = 0; j < N; j++) { if (mat[i][j] == 0) row += '.'; else row += 'Q'; } result.push_back(row); } results.push_back(result); } else { if (checkQueen(mat, N, row, col)) { //put queen here mat[row][col] = 1; //try next row nQueensSub(mat, N, row + 1, 0, results); mat[row][col] = 0; } //try next col if (col+1 < N) { nQueensSub(mat, N, row, col + 1, results); } } } vector<vector<string>> solveNQueens(int n) { int** mat = new int*[n]; for (int i = 0; i < n; i++) { mat[i] = new int[n]; for (int j = 0; j < n; j++) { mat[i][j] = 0; } } vector<vector<string>> results; nQueensSub(mat, n, 0, 0, results); for (int i = 0; i < n; i++) { delete[]mat[i]; } delete[] mat; return results; } }; |