手动模拟队列版本 C++ 代码

#include <cstring>
#include <iostream>
#include <algorithm>
#include <bitset>
#include <queue>

using namespace std;

const int N = 30010;

int n, m, hh, tt = -1;
int h[N], e[N], ne[N], idx;
int d[N], q[N];
bitset<N> f[N];

void add(int a, int b)
{
    e[idx] = b, ne[idx] = h[a], h[a] = idx ++ ;
}

void topsort()
{

    for (int i = 1; i <= n; i ++ )
        if (!d[i])
            q[++tt] = i;

    int k = 0;
    while (hh <= tt)
    {
        int t = q[hh++];

        for (int i = h[t]; ~i; i = ne[i])
        {
            int j = e[i];
            if (-- d[j] == 0)
                q[++tt] = j;
        }
    }
}

int main()
{
    cin >> n >> m;
    memset(h, -1, sizeof h);

    for (int i = 0; i < m; i ++ )
    {
        int a, b;
        cin >> a >> b;
        add(a, b);
        d[b] ++ ;
    }

    topsort();

    for (int i = n - 1; i >= 0; i -- )
    {
        int j = q[i];
        f[j][j] = 1;
        for (int k = h[j]; ~k; k = ne[k])
            f[j] |= f[e[k]];
    }

    for (int i = 1; i <= n; i ++ ) cout << f[i].count() << endl;

    return 0;
}