[Leetcode] N-Queens II
Follow up for N-Queens problem.
Now, instead outputting board configurations, return the total number of distinct solutions.
跟上一题一样,改下结果的显示方式。
1 class Solution { 2 public: 3 bool isValid(vector<string> &board, int x, int y) { 4 for (int i = 0; i < x; ++i) { 5 if (board[i][y] == 'Q') return false; 6 } 7 for (int i = 0; i < board.size(); ++i) { 8 for (int j = 0; j < board.size(); ++j) { 9 if (i != x && j != y && i-j == x-y && board[i][j] == 'Q') 10 return false; 11 if (i != x && j != y && i+j == x+y && board[i][j] == 'Q') 12 return false; 13 } 14 } 15 return true; 16 } 17 18 void solveHelper(int &res, vector<string> &board, int idx) { 19 if (idx == board.size()) { 20 ++res; 21 return; 22 } 23 for (int i = 0; i < board.size(); ++i) { 24 board[idx][i] = 'Q'; 25 if (isValid(board, idx, i)) { 26 solveHelper(res, board, idx + 1); 27 } 28 board[idx][i] = '.'; 29 } 30 } 31 32 int totalNQueens(int n) { 33 int res = 0; 34 vector<string> board; 35 string row; 36 for (int i = 0; i < n; ++i) { 37 row.push_back('.'); 38 } 39 for (int i = 0; i < n; ++i) { 40 board.push_back(row); 41 } 42 solveHelper(res, board, 0); 43 return res; 44 } 45 };