Rank of Tetris(topsort)

http://acm.hdu.edu.cn/showproblem.php?pid=1811

 #include <stdio.h>
 #include <string.h>
 #include <queue>
 #include <vector>
 using namespace std;
 const int N=;
 vector<int>V[N];
 queue<int>q;
 char oper[N];
 int in[N],f[N];
 int a[N],b[N];
 int n,m,sum;
 void init()
 {
     sum = n;
     while(!q.empty()) q.pop();
     for (int i = ; i <= n; i++)
     {
         f[i] = i;
         in[i] = ;
         V[i].clear();
     }
 }
 int Find(int x)
 {
     if(x!=f[x]) return f[x]=Find(f[x]);
     return x;
 }
 int Merge(int x,int y)
 {
     x = Find(x);
     y = Find(y);
     if(x!=y)
     {
         f[y] = x;
         return ;
     }
     return ;
 }
 void toposort()
 {
     int flag = ;
     for (int i = ; i < n; i++)
     {
         if(in[i]==&&Find(i)==i)
             q.push(i);
     }
     while(!q.empty())
     {
         if (q.size()>)flag = ;
         int u = q.front();
         q.pop();
         sum--;
         for (int i =  ; i < V[u].size(); i++)
         {
             if(--in[V[u][i]]==)
                 q.push(V[u][i]);
         }
     }
     if (sum > ) printf("CONFLICT\n");
     else if (flag) printf("UNCERTAIN\n");
     else printf("OK\n");
 }
 int main()
 {
     while(~scanf("%d%d",&n,&m))
     {
         init();
         int u,v;
         for (int i = ; i < m; i++)
         {
             scanf("%d %c %d",&a[i],&oper[i],&b[i]);
             if(oper[i]=='=')
             {
                 if(Merge(a[i],b[i]))
                     sum--;
             }
         }
         for (int i = ; i < m; i++)
         {
             if(oper[i]=='=') continue;
             u = Find(a[i]);
             v = Find(b[i]);
             if(oper[i]=='>')
             {
                 V[u].push_back(v);
                 in[v]++;
             }
             if(oper[i]=='<')
             {
                 V[v].push_back(u);
                 in[u]++;
             }
         }
         toposort();
     }
     return ;
 }