20分求找错

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<algorithm>
#include<cctype>
#include<cmath>
#include<cstdlib>
#include<queue>
#include<ctime>
#include<vector>
#include<set>
#include<map>
#include<stack>
using namespace std;
int low[110000],dfn[110000],ist[110000],belong[110000],cnt,tot;
vector<int>v[11000];
stack<int>a;
void tarjan(int x){
      dfn[x]=low[x]=++cnt;
      a.push(x);
      ist[x]=1;
      int i,j,k;
      for(i=0;i<v[x].size();i++)
         if(!dfn[v[x][i]]){
            tarjan(v[x][i]);
            low[x]=min(low[v[x][i]],low[x]);
         }else if(ist[v[x][i]]){
            low[x]=min(low[x],dfn[v[x][i]]);
         }
      if(dfn[x]==low[x]){
        tot++;
        while(1){
            int u=a.top();
            a.pop();
            ist[u]=0;
            belong[u]=tot;
            if(u==x)break;
        }
      }
}
int main()
{     int n,m,i,j,k,t;
      cin>>t;
      while(t--){
        cnt=0;
        tot=0;
        memset(low,0,sizeof(low));
        memset(dfn,0,sizeof(dfn));
        memset(ist,0,sizeof(ist));
        memset(belong,0,sizeof(belong));
        while(!a.empty())a.pop();
        cin>>n>>m;
        for(i=1;i<=m;i++){
            string s,t;
            cin>>s>>t;
            int x=0,y=0,xx=0,yy=0;
            int n1=s.length(),n2=t.length();
            if(s[0]=='m')x=n;
            for(j=1;j<n1;j++)
               xx=xx*10+(s[j]-'0');
            x+=xx;
            if(t[0]=='m')y=n;
            for(j=1;j<n2;j++)
               yy=yy*10+(t[j]-'0');
            y+=yy;
            if(y>n){
                v[x].push_back(y-n);
            }else v[x].push_back(y+n);
            if(x>n){
                v[y].push_back(x-n);
            }else v[y].push_back(x+n);
        }
        for(i=1;i<=2*n;i++)
           if(!dfn[i])
             tarjan(i);
        int ok=1;
        for(i=1;i<=n;i++)
           if(belong[i]==belong[i+n]){
             puts("BAD");
             ok=0;
             break;
           }
        if(ok)puts("GOOD");
      }
      return 0;
}