题目连接：Leetcode N-Queens II
解题思路：与 Leetcode 052 解法一样，只不过维护的答案不同。
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;
}
int dfs(int d, int n, int* pos) {
if (d >= n) { return 1; }
int ans = 0;
for (int i = 0; i < n; i++) {
if (check(d, i, pos) == false) continue;
pos[d] = i;
ans += dfs(d + 1, n, pos);
}
return ans;
}
int totalNQueens(int n) {
int* pos = new int[n];
int ans = dfs(0, n, pos);
delete pos;
return ans;
}
};
