不太明白各位大佬的做法，这道题直接连反边，做一遍topo排序不就行了吗？（求解）

C++ 代码

#include <bits/stdc++.h>
using namespace std;
const int N = 30010;
int n, m;
vector<int> vec[N];
int deg[N];
int w[N];
int a[N];
int q[N];
bitset<N> f[N];
void topo()
{
    int l = 0, r= -1;
    for(int i = 1; i <= n; i ++ )
    {
        if(!deg[i]) q[ ++ r] = i;
    }
    while(l <= r)
    {
        int u = q[l];
        f[u][u] = 1;
        for(int i = 0; i < vec[u].size(); i ++ )
        {
            int v = vec[u][i];
            f[v] |= f[u];
            if(!(--deg[v])) q[ ++ r] = v;
        }
        l ++;
    }
}
int main()
{
    cin >> n >> m;
    for(int i = 1; i <= m; i ++ )
    {
        int u, v;
        cin >> u >> v;
        vec[v].push_back(u);
        deg[u] ++;
    }
    topo();
    for(int i = 1; i <= n; i ++ )
    cout << f[i].count() << endl;
}