【洛谷-拓扑排序】P4017 最大食物链计数

#include<iostream>
#include<vector>
#include<queue>

using namespace std;

const int MO = 80112002;
const int maxn = 5005;
vector<int> edges[maxn];            //存的是能吃掉自身的生物序号
int n, m;
int inq[maxn],outq[maxn],f[maxn];           //入度，出度,到当前点共有多少条路径
queue<int> que;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int tmp1, tmp2,ans = 0;
    cin >> n >> m;
    for (int i = 0; i < m; i++) {
        cin >> tmp1 >> tmp2;
        edges[tmp1].push_back(tmp2);
        inq[tmp2]++;
        outq[tmp1]++;
    }
    //入度为零的入队
    for (int i = 1; i <= n; i++) {
        if (inq[i] == 0) {
            que.push(i);
            f[i] = 1;
        }
    }
    while (que.empty() == false) {
        int fro = que.front();
        que.pop();
        for (int i = 0; i < edges[fro].size(); i++) {
            int u = edges[fro][i];
            inq[u]--;
            if (inq[u] == 0)que.push(u);
            f[u] = (f[u] + f[fro]) % MO;
        }
    }
    for (int i = 1; i <= n; i++) {
        if (outq[i] == 0) {
            ans = (ans + f[i]) % MO;
        }
    }
    cout << ans;

    return 0;
}