poj 2762(scc)

强连通分量，这里是“或”，不是“且”，所以只要有入度或出度大于1的情况就输出no

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <queue>
#include <cmath>
#include <stack>
#include <set>
using namespace std;
#define hh printf("--------------\n");
const int maxn=1000+100;
const int maxm=6000+100;
int low[maxn],dfn[maxn];
int ncnt,ccnt;
int noc[maxn];
int hade[maxm];
bool vis[maxn],insk[maxn];
stack<int> sk;
struct note
{
    int to;
    int next;
} aa[maxm];
int n,m,k;
void addage(int fr,int to)
{
    aa[k].to=to;
    aa[k].next=hade[fr];
    hade[fr]=k++;
}
void tarjan(int u)
{
    ncnt++;
    low[u]=ncnt;
    dfn[u]=ncnt;
    sk.push(u);
    vis[u]=1;
    insk[u]=1;
    for(int i=hade[u]; i!=-1; i=aa[i].next)
    {
        int v=aa[i].to;
        if(!vis[v])
        {
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(insk[v])
        {
            low[u]=min(low[u],dfn[v]);
        }
    }
    if(low[u]==dfn[u])
    {
        int v;
        do
        {
            v=sk.top();
            sk.pop();
            insk[v]=0;
            noc[v]=ccnt;
        }
        while(v!=u);
        ccnt++;
    }
}
vector<set<int> > linefrom;
vector<set<int> > lineto;
void yasuo(int nn,int nc)
{
    linefrom.resize(nc);
    lineto.resize(nc);
    for(int u=1; u<=nn; u++)
        for(int i=hade[u]; i!=-1; i=aa[i].next)
        {
            int v=aa[i].to;
            int cu=noc[u];
            int cv=noc[v];
            if(cu!=cv)
            {
                linefrom[cv].insert(cu);
                lineto[cu].insert(cv);
            }
        }
}
void init()
{
    k=0;
    memset(hade,-1,sizeof(hade));
    memset(vis,0,sizeof(vis));
    memset(insk,0,sizeof(insk));
    memset(aa,0,sizeof(aa));
    memset(noc,0,sizeof(noc));
    while(sk.size()) sk.pop();
    linefrom.clear();
    lineto.clear();
    ncnt=0;
    ccnt=0;
}
int t;
int main()
{
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d%d",&n,&m);
        init();
        int a,b;
        for(int i=1; i<=m; i++)
        {
            scanf("%d%d",&a,&b);
            addage(a,b);
        }
        for(int i=1; i<=n; i++)
            if(!vis[i]) tarjan(i);
        yasuo(n,ccnt);
        int z_in=0,z_out=0;
        for(int i=0; i<ccnt; i++)
        {
            if(linefrom[i].empty()) z_in++;
            if(lineto[i].empty()) z_out++;
        }
        if(z_out>1||z_in>1) printf("No\n");
        else printf("Yes\n");
    }
    return 0;
}