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

 void topsort() {
     queue<int> q;
     for(int i = ; i <= n; i++) {
         if(InDeg[i] == ) {
             q.push(i);
         }
     }
     int x;
     while(!q.empty()) {
         x = q.front(), q.pop();
         int s = G[x].size();
         for(int i = ; i < s; i++) {
             if(--InDeg[G[x][i]] == ) {
                 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 = ; i <= n; i++) {
             G[i].clear();
         }
         memset(InDeg, , sizeof(InDeg));
         memset(virus, , sizeof(virus));
         for(int i = ; i < k; i++) {
             scanf("%d", &x);
             virus[x] = ;
         }
         for(int i =  ; i < m; i++) {
             scanf("%d%d", &u, &v);
             G[u].push_back(v);
             InDeg[v]++;
         }
         topsort();
         int ans = ;
         for(int i = ; i <= n; i++) {
             ans = (ans + virus[i]) % mod;
         }
         printf("%d\n", ans);
     }
     return ;
 }