代码：

#include<bits/stdc++.h>

using namespace std;

const int N = 55;

int t, n, m;

double dis[N], in[N];
bool vis[N];

int head[N], tot;


inline int read() {
	int x = 0, f = 1;
    char ch = getchar();
	while(ch < '0' || ch > '9'){
        if(ch == '-'){
            f = -1;
        }
        ch = getchar();
    }
	while(ch >= '0' && ch <= '9'){
        x = x * 10 + ch - 48;
        ch = getchar();
    }
	return x * f;
}

struct Node{
	int to, next;
	double w;
}edges[N * 2];

void add(int u, int v, double w){
	tot++;
	edges[tot].to = v;
	edges[tot].w = w;
	edges[tot].next = head[u];
	head[u] = tot;
}

bool spfa(double mid){
	queue<int> q;
	memset(vis, 0, sizeof(vis));
	for(int i = 1; i <= n; i++){
		dis[i] = 0;
		q.push(i);
		vis[i] = true;
	}
	while(!q.empty()){
		int x = q.front();
		q.pop();
		vis[x] = false;
		for(int i = head[x]; i; i = edges[i].next){
			if(dis[x] + (edges[i].w - mid) < dis[edges[i].to]){
				dis[edges[i].to] = dis[x] + (edges[i].w - mid);
				in[edges[i].to] = in[x] + 1;
				if(in[edges[i].to] >= n){
				    return true;
				}
				if(!vis[edges[i].to]){
					vis[edges[i].to] = true;
					q.push(edges[i].to);
				}
			}
		}
	}
	return false;
}

int main(){
	t = read();
	for(int p = 1; p <= t; p++){
		memset(head, 0, sizeof(head));
		memset(in, 0, sizeof(in));
        n = read(), m = read();
		double l = 1e9, r = -1e9;
		for(int i = 1; i <= m; i++){
			int u, v;
			double w;
            u = read();
            v = read();
			w = read();
			l = min(l, w);
			r = max(r, w);
			add(u, v, w);
		}
        l--, r++;
		double tmp = r;
		double eps = 1e-5;
		while(l + eps < r){
			double mid = (l + r) / 2.0;
			if(spfa(mid)){
				r = mid;
			}
			else{
				l = mid;
			}
		}
		if(tmp == r){
			printf("Case #%d: No cycle found.", p);
		}
		else{
			printf("Case #%d: %0.2f", p, r);
		}
		if(p <= t - 1){
			printf("\n");
		}
	}
	return 0;
}