Legal or Not 拓扑加邻接表 hdu

#include <stdio.h>#include <cstring>#include <queue>#include <iostream>using namespace std;const int maxn=101;struct edge{    int from,to,next;} e[maxn<<1];int head[maxn];int in[maxn];int n,t,m;bool topsort(){    queue <int> q;    for(int i=0; i<n; i++)        if(in[i]==0) q.push(i);    int nodenum=0;    while(!q.empty())    {        int v=q.front();        q.pop();        nodenum++;        for(int i=head[v]; i!=-1; i=e[i].next)        {            int u=e[i].to;            in[u]--;            if(in[u]==0)                q.push(u);        }    }    if(nodenum<n) return false;    return true;}void add(int i,int j){    e[t].from=i;    e[t].to=j;    e[t].next=head[i];    head[i]=t++;}int main(){    int a,b;    while(scanf("%d%d",&n,&m)==2)    {        if(n==0&&m==0) break;        t=0;        memset(in,0,sizeof(in));        memset(head,-1,sizeof(head));        for(int i=1; i<=m; i++)        {            scanf("%d%d",&a,&b);            add(a,b);            in[b]++;        }        if(topsort()) printf("YES\n");        else printf("NO\n");    }    return 0;}