UVA11090 Going in Cycle!! 传送门

#include<cstdio>
#include<cstring>
#include<set>
#include<algorithm>
#include<map>
#include<iostream>
#include<cstdlib>
#include<queue>
#include<deque>
#include<string>
#include<stack>
#include<vector>
#include<cmath>
using namespace std;
#define lck_max(a,b) ((a)>(b)?(a):(b))
const int maxn=505;
const double eps=1e-3,INF=1e9;
inline int read()
{
    int xs=0,kr=1;char ls;
    ls=getchar();
    while(!isdigit(ls))
    {
        if(!(ls^45))
            kr=-1;
        ls=getchar();
    }
    while(isdigit(ls))
    {
        xs=(xs<<1)+(xs<<3)+(ls^48);
        ls=getchar();
    }
    return kr*xs;
}
int n,m,u,v;double w;
struct hh
{
    int nex,to;
    double w;
}t[maxn];
int head[maxn],cnt;
inline void add(int nex,int to,int w)
{
    t[++cnt].nex=head[nex];
    t[cnt].to=to;
    t[cnt].w=w;
    head[nex]=cnt;
}
double d[maxn];int num[maxn];bool inq[maxn];
queue<int>q;
inline bool spfa(double mid)
{
    for(int i=1;i<=n;i++) d[i]=INF;
    memset(inq,0,sizeof(inq));
    memset(num,0,sizeof(num));
    for(int i=1;i<=n;i++) d[i]=0.0,inq[i]=true,q.push(i);
    while(!q.empty())
    {
        int u=q.front();q.pop();inq[u]=false;
        for(int i=head[u];i;i=t[i].nex)
        {
            int v=t[i].to;double w=t[i].w-mid;
            if(d[v]>d[u]+w)
            {
                d[v]=d[u]+w;
                if(!inq[v])
                {
                    inq[v]=true,q.push(v);
                    if(++num[v]>n) return true;
                }
            }
        }
    }
    return false;
}
int T,cas;
int main()
{
    T=read();
    while(T--)
    {
        cas++;
        printf("Case #%d: ",cas);
        n=read();m=read();
        memset(head,0,sizeof(head));
        double l=0,r=0;
        for(int i=1;i<=m;i++)
            u=read(),v=read(),w=read(),add(u,v,w),r=lck_max(r,w);
        if(!spfa(r+1)) puts("No cycle found.");
        else
        {
            while(r-l>eps)
            {
                double mid=(l+r)/2;
                if(spfa(mid)) r=mid;
                else l=mid;
            }
            printf("%.2f
",l);
        }
    }
return 0;
}