code：

#include <bits/stdc++.h>
using namespace std;
void read(int &x) {
    int s=0,w=1;
    char c=getchar();
    while(c<'0'||c>'9') {
        if(c=='-') {
            w=-1;
        }
        c=getchar();
    }
    while(c>='0'&&c<='9') {
        s=s*10+c-'0';
        c=getchar();
    }
    x=s*w;
    return;
}
int w;
int n,m;
struct edge {
    int next,to,wt;
} e[2010];
int head[2010],tot;
int dist[110],cnt[110];
bool vis[110];
inline void add(int u,int v,int w) {
    tot++;
    e[tot].to=v;
    e[tot].next=head[u];
    head[u]=tot;
    return ;
}
inline bool SPFA(int s) {
    queue<int> q;
    dist[s] = 0;
    vis[s] = 1;
    q.push(s);
    while (q.size() > 0) {
        int x = q.front();
        vis[x] = 0;
        q.pop();
        for (int i = head[x]; i; i = e[i].next) {
            int y = e[i].to;
            if (dist[x] + e[i].wt < dist[y]) {
                dist[y] = dist[x] + e[i].wt;
                cnt[y] = cnt[x] + 1;
                if (cnt[y] > n) {
                    return true;
                }
                if (!vis[y]) {
                    vis[y] = 1;
                    q.push(y);
                }
            }
        }
    }
    return false;
}
int s,t,v;
int main() {
    read(w);
    for(int test=1; test<=w; test++) {
        memset(e,0,sizeof(e));
        memset(head,0,sizeof(head));
        memset(dist,0x3f3f3f3f,sizeof(dist));
        memset(vis,0,sizeof(vis));
        read(n);
        read(m);
        for(int i=1; i<=m; i++) {
            read(s);
            read(t);
            read(v);
            add(s-1,t,w);
            add(t,s-1,-w);
        }
        for(int i=1; i<=n; i++) {
            add(n+1,i,0);
        }
        if(SPFA(n+1)) {
            printf("true\n");
        } else {
            printf("false\n");
        }
    }
    return 0;
}

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