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