hdu1269强连通水题 如果让我说：我只能说，实力决定一切

#include<iostream>#include<algorithm>#include<cstdio>#include<string.h>#include<vector>#include<stack>#define maxn 11111using namespace std;int dfn[maxn],low[maxn],vis[maxn],belong[maxn],ind[maxn],outd[maxn];int sum,tem;vector<int>gra[maxn];stack<int>S;int MIN(int a,int b){    return a>b?b:a;}void tarjan(int pox){    vis[pox]=2;    dfn[pox]=low[pox]=++sum;    S.push(pox);    for(int i=0; i<gra[pox].size(); i++)    {        int t=gra[pox][i];        if(!dfn[t])        {            tarjan(t);            low[pox]=MIN(low[pox],low[t]);        }        else if(vis[t]==2)        {            low[pox]=MIN(low[pox],dfn[t]);        }    }    if(dfn[pox]==low[pox])    {        tem++;        while(!S.empty())        {            int gh=S.top();            S.pop();            if(gh==pox)                break;        }    }}int main(){    int N,M;    int a,b;    while(scanf("%d%d",&N,&M),N+M)    {        tem=sum=0;        memset(vis,0,sizeof(vis));        memset(dfn,0,sizeof(dfn));        memset(low,0,sizeof(low));        for(int i=0; i<maxn; i++)            gra[i].clear();        while(!S.empty())            S.pop();        for(int i=0; i<M; i++)        {            scanf("%d%d",&a,&b);            gra[a].push_back(b);        }        for(int i=1; i<=N; i++)            if(!dfn[i])                tarjan(i);        if(tem==1)            printf("Yes\n");        else            printf("No\n");    }    return 0;}