1 /* 2     Name:hdoj-3342-Legal or Not 3     Copyright: 4     Author: 5     Date: 2018/4/11 15:59:18 6     Description: 7         判断是否存在环  8 */ 9 #include 
     
      10 #include 
      
       11 #include 
       
        12 #include 
        
         13 #include 
         
          14 using namespace std;15 const int MAXN = 1e+5;16 int du[MAXN], n , m, L[MAXN];17 vector
          
            g[MAXN];18 bool topsort() {19 memset(du, 0, sizeof(du));20 for (int i=0; i
           

Q;27 for (int i=0; i

>n>>m && (m || n)) {50 memset(L, 0, sizeof(L));51 memset(g, 0, sizeof(g));52 for (int i=0; i

>a>>b;55 g[a].push_back(b);56 }57 if (topsort() == 1) cout<<"YES"<