Created
October 30, 2016 06:58
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ABC 041-D 徒競走
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#include<iostream> | |
using namespace std; | |
#define int long long | |
int N, M; | |
int memo[1<<16]; | |
int g[16][16]; | |
int rec(int S){ | |
if(memo[S]!=0) return memo[S]; | |
if(S==0){ | |
return 1; | |
} | |
int ret=0; | |
for(int j=0; j<N; j++){ | |
if(!((S>>j)&1)) continue; | |
for(int k=0; k<N; k++){ | |
if((S>>k)&1 && g[j][k]){ | |
goto failed; | |
} | |
} | |
ret+=rec(S-(1<<j)); | |
failed:; | |
} | |
return memo[S]=ret; | |
} | |
signed main(){ | |
cin>> N>> M; | |
for(int i=0; i<M; i++){ | |
int a, b; | |
cin>> a>> b; | |
g[a-1][b-1]=1; | |
} | |
cout<< rec((1<<N)-1)<< endl; | |
return 0; | |
} |
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