052.N-Queens II

// 没有太大意义，和51题重复，只需要计数或者输出vector的大小即可
 1 class Solution {
 2 public:
 3     int totalNQueens(int n) {
 4         vector<vector<string>> result;
 5         vector<int> pos(n, -1);
 6         vector<int> isColumnSafe(n, 1);
 7         vector<int> isDiag1Safe(2 * n - 1, 1); // 主对角线
 8         vector<int> isDiag2Safe(2 * n - 1, 1); // 斜对角线
 9         checkPos(result, pos, isColumnSafe, isDiag1Safe, isDiag2Safe, 0, n);
10         return result.size();
11     }
12 private:
13 void checkPos(
14     vector<vector<string>>& result,
15     vector<int>& pos,
16     vector<int>& isColumnSafe,
17     vector<int>& isDiag1Safe,
18     vector<int>& isDiag2Safe,
19     int i,
20     int n
21 )
22 {
23     for (int j = 0; j < n; ++j) {
24         bool flag = isColumnSafe[j] && isDiag1Safe[i - j + n - 1] && isDiag2Safe[i + j];
25         if (flag) {
26             isColumnSafe[j] = 0;
27             isDiag1Safe[i - j + n - 1] = 0;
28             isDiag2Safe[i + j] = 0;
29             pos[i] = j;
30             if (i == n - 1) {
31                 vector<string> vec(n, string(n, ‘.‘));
32                 int cnt = 0;
33                 for (int k = 0; k < n; ++k) {
34                     vec[cnt ++][pos[k]] = ‘Q‘;
35                 }
36                 result.push_back(vec);
37                 for (int i = 0; i < n; ++i) {
38                     cout << vec[i] << endl;
39                 }
40                 cout << endl;
41             }
42             else {
43                 checkPos(result, pos, isColumnSafe, isDiag1Safe, isDiag2Safe, i + 1, n);
44             }
45             isColumnSafe[j] = 1;
46             isDiag1Safe[i - j + n - 1] = 1;
47             isDiag2Safe[i + j] = 1;
48         }
49     }
50 }
51 };