只过了第一个点...

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <queue>
using namespace std;
const int N=1e5;
const int inf=2e7;
queue<int> q;
bool v[N],f;
int ver[N],head[N],nxt[N],edge[N],n,m,tot,d[N],cnt[N],k,ans,w;
inline int read(){
  int x=0,f=1;char ch=getchar();
  while(ch>'9'||ch<'0'){if(ch=='-')f=-1;ch=getchar();}
  while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+ch-'0';ch=getchar();}
  return x*f;
}
inline void add(int x,int y,int z){
  ver[++tot]=y,edge[tot]=z,nxt[tot]=head[x],head[x]=tot;
}
inline bool spfa(int s){
  for(int i=1;i<=n;i++)
    cnt[i]=0,v[i]=0,d[i]=-inf;
  q.push(s);v[s]=1;d[s]=0;
  while(q.size()){
    int x=q.front();q.pop();
    v[x]=0;
    for(int i=head[x];i;i=nxt[i]){
      int y=ver[i],z=edge[i];
      if(d[y]<d[x]+z){
	d[y]=d[x]+z;
	cnt[y]=cnt[x]+1;
	if(cnt[y]>=n)
	  return 0;
	if(!v[y]){q.push(y);v[y]=1;}
      }
    }
  }
  return 1;
}
int main(){
  w=read();
  while(w--){
    n=read();m=read();
    memset(head,0,sizeof(head));
    for(int i=1;i<=m;i++){
      int s,t,v;
      s=read();t=read();v=read();
      add(s-1,t,v);
      add(t,s-1,-v);
    }
    f=0;
    for(int i=0;i<=n;i++){
      if(!cnt[i]){
	if(!spfa(i)){
	  f=1;break;
	}
      }
    }
    if(!f) cout<<"true"<<endl;
    else cout<<"false"<<endl;
  }
  return 0;
}