JZYZOJ 1388 旅游 状压dp

 1 #include<iostream>  
 2 #include<cstdio>  
 3 #include<cstring>  
 4 #include<algorithm>  
 5 #include<cmath>
 6 #include<queue>
 7 using namespace std;
 8 const int maxn=30;
 9 int n,m;
10 int a[maxn]={};
11 long long f[(1<<17)+10]={};
12 int main(){
13     scanf("%d%d",&n,&m);int x,y;
14     for(int i=1;i<=m;i++){
15         scanf("%d%d",&x,&y);
16         a[x]|=(1<<(y-1));
17     }
18     int ma=1<<n;f[0]=1;
19     for(int i=1;i<ma;i++){
20         for(int j=0;j<n;j++){
21             if((1<<j)&i){
22                 y=i-(1<<j);
23                 if((a[j+1]&(~y))==0){
24                     f[i]+=f[y];
25                 }
26             }
27         }
28     }
29     printf("%I64d\n",f[ma-1]);
30     return 0;
31 }