hihoCoder #1175 : 拓扑排序·二

题目链接：http://hihocoder.com/problemset/problem/1175

代码实现如下：

#include <queue>
#include <cstdio>
#include <cstring>
using namespace std;

const int maxn = 1e5 + 7;
const int mod = 142857;
int n, m, k, u, v, x;
int InDeg[maxn], virus[maxn];
vector<int> G[maxn];

void topsort() {
    queue<int> q;
    for(int i = 1; i <= n; i++) {
        if(InDeg[i] == 0) {
            q.push(i);
        }
    }
    int x;
    while(!q.empty()) {
        x = q.front(), q.pop();
        int s = G[x].size();
        for(int i = 0; i < s; i++) {
            if(--InDeg[G[x][i]] == 0) {
                q.push(G[x][i]);
            }
            virus[G[x][i]] = (virus[G[x][i]] + virus[x]) % mod;
        }
    }
}

int main() {
    while(~scanf("%d%d%d", &n, &m, &k)) {
        for(int i = 0; i <= n; i++) {
            G[i].clear();
        }
        memset(InDeg, 0, sizeof(InDeg));
        memset(virus, 0, sizeof(virus));
        for(int i = 0; i < k; i++) {
            scanf("%d", &x);
            virus[x] = 1;
        }
        for(int i = 0 ; i < m; i++) {
            scanf("%d%d", &u, &v);
            G[u].push_back(v);
            InDeg[v]++;
        }
        topsort();
        int ans = 0;
        for(int i = 1; i <= n; i++) {
            ans = (ans + virus[i]) % mod;
        }
        printf("%d
", ans);
    }
    return 0;
}