49 lines
1.1 KiB
C++
49 lines
1.1 KiB
C++
#include <iostream>
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#include <cstdio>
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#include <cstdlib>
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#include <cstring>
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#include <string>
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#include <queue>
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#include <algorithm>
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#include <map>
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#include <cmath>
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#include <iomanip>
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#define INF 99999999
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typedef __int64 LL;
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using namespace std;
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const int MAX=(1<<18)+10;
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int n,m;
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LL dp[MAX][20];
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bool edge[20][20];
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void DP(){
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int bit=1<<n;
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memset(dp,0,sizeof dp);
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dp[1][0]=1;
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for(int i=1;i<bit;++i){
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for(int j=0;j<n;++j){
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if(dp[i][j] == 0)continue;
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for(int k=1;k<n;++k){
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if(i&(1<<k))continue;
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if(!edge[j][k])continue;
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dp[i|(1<<k)][k]+=dp[i][j];
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}
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}
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}
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LL sum=0;
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for(int i=0;i<n;++i)if(edge[0][i])sum+=dp[bit-1][i];
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printf("%I64d\n",sum);
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}
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int main(){
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int u,v;
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while(~scanf("%d%d",&n,&m)){
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memset(edge,false,sizeof edge);
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for(int i=0;i<m;++i){
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scanf("%d%d",&u,&v);
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--u,--v;
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edge[u][v]=edge[v][u]=true;
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}
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DP();
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}
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return 0;
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}
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