HDU 2553 N皇后问题

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 int uplimit,ret,n;
 4 void dfs(int row,int ld,int rd){
 5    if(row == uplimit) ++ret;
 6     else{
 7         int pos = uplimit & (~(row|ld|rd));
 8         while(pos){
 9             int p = pos&(-pos);
10             pos ^= p;
11             dfs(row|p,(ld|p)<<1,(rd|p)>>1);
12         }
13     }
14 }
15 int main(){
16     while(scanf("%d",&n),n){
17         uplimit = (1<<n)-1;
18         ret = 0;
19         dfs(0,0,0);
20         printf("%d\n",ret);
21     }
22     return 0;
23 }