题目来自:点击这里
#include<cstdio>
#include<iostream>
#include<cstring>
#include<queue>
#include<algorithm>
using namespace std;
const int maxn=5005;
const int maxm=500005;
const int mod=80112002;
int in[maxn],head[maxn],num=0,ans=0,out[maxn],vis[maxn];
struct node{
int next,to;
}kkk[maxm];
void addedge(int u,int v){
kkk[++num].next=head[u];
kkk[num].to=v;
head[u]=num;
}
int main()
{
int n,m;
scanf("%d%d",&n,&m);
for(int i=0;i<m;++i){
int u,v;
scanf("%d%d",&u,&v);
addedge(u,v);
++out[u],++in[v];
}
queue<int>q;
for(int i=1;i<=n;++i){
if(!in[i]){
vis[i]=1;
q.push(i);
}
}
while(!q.empty()){
int u=q.front();q.pop();
for(int i=head[u];i;i=kkk[i].next){
int v=kkk[i].to;
vis[v]=(vis[v]+vis[u])%mod;
--in[v];
if(!in[v]){
if(!out[v]){
ans=(ans+vis[v])%mod;
}
else{
q.push(v);
}
}
}
}
printf("%d\n",ans);
return 0;
}