传送门

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#define re register 
using namespace std;
const int maxn = 2005;
const int maxm = 3005;

inline int read(){
    char ch = getchar();
    int f = 1 , x = 0 ;
    while(ch > '9' || ch < '0') {if(ch == '-' ) f = -1 ; ch = getchar();}
    while(ch >= '0' && ch <= '9'){x = (x << 1) + (x << 3) + ch - '0' ;ch = getchar();}
    return x * f;
}

int T,n,m,u,v,w;
int head[maxn],tot;
bool flag;
 
struct Edge{
    int from , to , next , val;
}edge[maxm << 1];

inline void add(int u , int v , int w){
    edge[++tot].from = u ;
    edge[tot].to = v;
    edge[tot].val = w;
    edge[tot].next = head[u];
    head[u] = tot;
}

int dis[maxn],num[maxn];
bool vis[maxn];

inline bool spfa(int s){
    for(re int i = 1 ; i <= n ; ++i)  dis[i] = 1e9 ;
    queue<int> q;
    q.push(s);
    dis[s] = 0;
    num[s]++;
    vis[s] = true;
    while(!q.empty()){
        int cur = q.front();
        q.pop(); vis[cur] = 0;
        for(re int i = head[cur] ; i ; i = edge[i].next) {
            int v = edge[i].to ;
            if(dis[v] > dis[cur] + edge[i].val) {
                dis[v] = dis[cur] + edge[i].val;
                if(!vis[v]) {
                    q.push(v);
                    num[v]++;
                    vis[v] = true;
                    if(num[v] > n)  return false;
                }
            }
        }
    }
    return true;
}           

int main(){
    T = read();
    while(T--){
        memset(dis , 0 , sizeof(dis));
        memset(edge , 0 ,sizeof(edge));
        memset(num , 0 , sizeof(num));
        memset(head , 0 , sizeof(head));
        memset(vis , 0 , sizeof(vis));
        tot = 0;
        flag = 0;
        n = read(); m = read();
        for(re int i = 1 ; i <= m ; ++i){
            u = read(); v = read(); w = read();
            if(w < 0) add(u , v , w);
            else {
                add(u , v , w);
                add(v , u , w);
            }
        }
        if(spfa(1)) printf("N0\n");
        else printf("YE5\n");
    }
    return 0;
}