Legal or Not HDU - 3342 (拓扑排序)

 注意点： 输入数据中可能有重复，需要进行处理！

 #include <stdio.h>
 #include <iostream>
 #include <cstring>
 #include <vector>
 #include <algorithm>
 #include <sstream>

 using namespace std;

 int n, m;

 int indegree[];
 int g[][]; 

 int main()
 {
     while(scanf("%d %d", &n, &m) != EOF)
     {
         if(n ==  && m == )
             break;

         memset(indegree, , sizeof(indegree));
         memset(g, , sizeof(g));

         int a, b;
         for(int i = ; i <= m; ++i)
         {
             scanf("%d %d", &a, &b);

             if(g[a][b] == )    // 输入中有可能有反复输入如1,2；1,2这种情况！！！
             {
                 g[a][b] = ;
                 indegree[b]++;
             }

         }

         int cnt = ;

         for(int k = ; k < n; ++k)
         {
             int i, j;
             for(i = ; i < n; ++i)
             {
                 if(indegree[i] == )
                 {
                     indegree[i] = -;
                     cnt++;
                     break;
                 }
             } 

             for(j = ; j < n; ++j)
             {
                 if(g[i][j] == )
                 {
                     indegree[j]--;
                     g[i][j] == ;
                 }
             }
         }

         if(cnt == n)
             cout << "YES" << endl;
         else
             cout << "NO" << endl;
     }

     return ;
 }