题目连接：Leetcode 051 N-Queens
解题思路：枚举每一行Queen的位置，保证当前行的Queen不与前面行的Queen冲突。
class Solution { public: bool check(int x, int y, int* pos) { for (int i = 0; i < x; i++) { if (y == pos[i]) return false; if (y - x == pos[i] - i) return false; if (x + y == pos[i] + i) return false; } return true; } void dfs(int d, int n, int* pos, vector<vector<string>>& ans, vector<string>& m) { if (d >= n) { ans.push_back(m); return; } for (int i = 0; i < n; i++) { if (check(d, i, pos) == false) continue; pos[d] = i; m[d][i] = 'Q'; dfs(d + 1, n, pos, ans, m); m[d][i] = '.'; } } vector<vector<string>> solveNQueens(int n) { string s = ""; for (int i = 0; i < n; i++) s = s+'.'; vector<string> m; for (int i = 0; i < n; i++) m.push_back(s); vector<vector<string>> ans; int* pos = new int[n]; dfs(0, n, pos, ans, m); delete pos; return ans; } };