HDU 1269 裸奔的强联通分量

#include <cstdio>
#include <cmath>
#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <string>
#include <queue>
#include <stack>
#include <cstring>
#define CL(a,b) memset(a,b,sizeof(a))
#define ll __int64
#define TEST cout<<"TEST   ***"<<endl;
#define INF 0x7ffffff0
#define MOD 1000000007
using namespace std;

typedef struct myedge
{
    int e,next;
}E;
E edge[100010];
stack <int> st;

int head[10010],ct,tim;
int ti[10010],lo[10010],ins[10010],n,m;

void inithead()
{
    CL(head,-1);
    tim=0;
    ct=0;
}

void addedge(int s,int e)
{
    edge[ct].e=e;edge[ct].next=head[s];head[s]=ct++;
}

void targan(int i)
{
    tim++;
    ti[i]=tim;lo[i]=tim;
    st.push(i);
    ins[i]=1;
    int p=head[i];
    int v;
    while(p!=-1)
    {
        v=edge[p].e;
        if(ins[v]==1)
        {
            lo[i]=min(lo[v],lo[i]);
        }
        else if(ti[v]==0)
        {
            targan(v);
            lo[i]=min(lo[i],lo[v]);
        }
        p=edge[p].next;
    }
    if(lo[i]==ti[i])
    {
        while(!st.empty()&&lo[st.top()]==ti[i])
        {
            ins[st.top()]=0;
            st.pop();
        }
    }
}


int main()
{
    while(scanf("%d %d",&n,&m)!=EOF)
    {
        if(n==0&&m==0)break;
        int i,j,a,b;
        inithead();
        CL(lo,0);
        CL(ti,0);
        CL(ins,0);
        for(i=0;i<m;i++)
        {
            scanf("%d %d",&a,&b);
            addedge(a,b);
        }
        targan(1);
        int re=0;
        for(i=1;i<=n;i++)
        {
            if(lo[i]==ti[i])re++;
        }
  //      cout<<re<<endl;
        if(re==1)printf("Yes\n");
        else printf("No\n");
    }
    return 0;
}