Proving Equivalences 强连通

#include<bits/stdc++.h>
using namespace std;
//input by bxd
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define repp(i,a,b) for(int i=(a);i>=(b);--i)
#define RI(n) scanf("%d",&(n))
#define RII(n,m) scanf("%d%d",&n,&m)
#define RIII(n,m,k) scanf("%d%d%d",&n,&m,&k)
#define RS(s) scanf("%s",s);
#define ll long long
#define pb push_back
#define REP(i,N)  for(int i=0;i<(N);i++)
#define CLR(A,v)  memset(A,v,sizeof A)
//////////////////////////////////
#define inf 0x3f3f3f3f
const int N=20000+5;
int head[10*N],pos;
struct Edge
{
    int to,nex;
}edge[10*N];
void add(int a,int b)
{
    edge[++pos].nex=head[a];
    head[a]=pos;
    edge[pos].to=b;
}
int dfn[N],low[N],tot,vis[N],ind,Stack[N],cnt,belong[N];
int in[N],out[N];
int init()
{
    CLR(head,0);
    CLR(dfn,0);
    CLR(low,0);
    CLR(vis,0);
    CLR(Stack,0);
    CLR(belong,0);
    CLR(in,0);
    CLR(out,0);
    cnt=ind=tot=pos=0;
}
void tarjan(int x)
{
    dfn[x]=low[x]=++tot;
    Stack[++ind]=x;
    vis[x]=1;
    for(int i=head[x];i;i=edge[i].nex)
    {
        int v=edge[i].to;
        if(!dfn[v])
        {
            tarjan(v);low[x]=min(low[x],low[v]);
        }
        else if(vis[v])
            low[x]=min(low[x],low[v]);
    }
    if(low[x]==dfn[x])
    {
        cnt++;
        int v;
        do
        {
            v=Stack[ind--];
            vis[v]=0;
            belong[v]=cnt;
        }
        while(x!=v);
    }
}

int main()
{
    int n,m;
    while(RII(n,m)==2)
    {
        init();
        rep(i,1,m)
        {
            int a,b;RII(a,b);
            add(a,b);
        }
        rep(i,1,n)
        if(!dfn[i])
            tarjan(i);

            int Cnt=0;
        rep(i,1,n)
        {
            int u=belong[i];
            for(int j=head[i];j;j=edge[j].nex)
            {
                int v=belong[edge[j].to];
                if(u!=v)
                out[u]++,in[v]++;
            }
        }
        int q=0,w=0;
        rep(i,1,cnt)
        { 
            if(!in[i])q++;
            if(!out[i])w++;
        }
        if(cnt==1)
            cout<<0<<endl;
        else 
       cout<<max(q,w)<<endl;
    }
    return 0;
}