https://blog.csdn.net/zhouzi2018/article/details/81610804

#include<iostream>
#include<cstdio>
#include<vector>
#include<cstring>

using namespace std;

const int maxn=100;
int n,m;
vector<int> mp[maxn];
vector<int> rmp[maxn];
int vis[maxn];
vector<int> vs;
int cmp[maxn];
void dfs(int u)
{
    vis[u] = 1;
    for(int i = 0;i<mp[u].size();i++)
    {
        if(vis[mp[u][i]] == 0)
        {
            dfs(mp[u][i]);
        }
    }
    vs.push_back(u);
}
void rdfs(int u,int k)
{
    vis[u] = 1;
    cmp[u] = k;
    for(int i=0;i<rmp[u].size();i++)
    {
        if(vis[rmp[u][i]] == 0)
        {
            rdfs(rmp[u][i],k);
        }
    }
}
int scc()
{
    memset(vis,0,sizeof(vis));
    vs.clear();
    for(int i = 1;i<=n;i++)
    {
        if(vis[i] == 0)
        {
            dfs(i);
        }
    }
    memset(vis,0,sizeof(vis));
    int ans = 0;
    for(int i = vs.size()-1;i>=0;i--)
    {
        if(vis[vs[i]] == 0)
        {
            rdfs(vs[i],ans++);
        }
    }
    return ans;
}
int main()
{
    while(scanf("%d",&n)!=EOF)
    {
        if(n == 0) break;
        scanf("%d",&m);
        for(int i=1;i<=n;i++)
        {
            mp[i].clear();
            rmp[i].clear();
        }
        for(int i=1;i<=m;i++)
        {
            int u,v;
            scanf("%d%d",&u,&v);
            mp[u].push_back(v);
            rmp[v].push_back(u);
        }
        int ans = scc();
        printf("%d\n",ans);
    }
}