ZOJ 3687 The Review Plan I 容斥原理

一道纯粹的容斥原理题！！不过有一个trick，就是会出现重复的，害我WA了几次！！

代码：

 

#include<iostream> #include<cstdio> #include<cmath> #include<algorithm> #include<cstring> #include<set> #include<vector>

#define ll long long

#define mod 55566677

using namespace std; int p[52],ans; int m,n; bool visd[52],visc[52],vis[52][52]; struct point { int a,b; }q[30]; void dfs(int s,int i,int f) { ans=(ans+f*p[n-s])%mod; while(ans<0) ans=(ans+mod)%mod; for(int k=i+1;k<m;k++){ if(!visd[q[k].a]&&!visc[q[k].b]){ visd[q[k].a]=1; visc[q[k].b]=1; dfs(s+1,k,-f); visd[q[k].a]=0; visc[q[k].b]=0; } } } int main() { int i,a,b,j; p[0]=p[1]=1; for(i=2;i<=50;i++) p[i]=((ll)p[i-1]*i)%mod; while(scanf("%d%d",&n,&m)!=EOF){ memset(vis,0,sizeof(vis)); memset(visd,0,sizeof(visd)); memset(visc,0,sizeof(visc)); for(j=i=0;i<m;i++){ scanf("%d%d",&a,&b); if(!vis[a][b]){ vis[a][b]=1; q[j].a=a; q[j++].b=b; } } m=j; ans=0; for(i=0;i<m;i++){ visd[q[i].a]=1; visc[q[i].b]=1; dfs(1,i,1); visd[q[i].a]=0; visc[q[i].b]=0; } ans=(p[n]-ans)%mod; while(ans<0) ans=(ans+mod)%mod; printf("%d\n",ans); } return 0; }

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