UVA-11090 Going in Cycle!! （平均值最大回路）

# include<iostream>
# include<cstdio>
# include<queue>
# include<vector>
# include<cstring>
# include<algorithm>
using namespace std;

const double inf=1e30;
struct Edge
{
    int to,nxt;
    double w;
};
Edge e[10000];
double dist[55];
int vis[55],inq[55],head[55],n,cnt;

void add(int u,int v,double w)
{
    e[cnt].to=v;
    e[cnt].w=w;
    e[cnt].nxt=head[u];
    head[u]=cnt++;
}

bool judge(double M)
{
    queue<int>q;
    memset(vis,0,sizeof(vis));
    memset(inq,0,sizeof(inq));
    for(int i=0;i<n;++i){
        dist[i]=0;
        vis[i]=inq[i]=1;
        q.push(i);
    }
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        inq[u]=0;
        for(int i=head[u];i!=-1;i=e[i].nxt){
            if(dist[e[i].to]>dist[u]+e[i].w-M){
                dist[e[i].to]=dist[u]+e[i].w-M;
                if(!inq[e[i].to]){
                    q.push(e[i].to);
                    inq[e[i].to]=1;
                    if(++vis[e[i].to]>n)
                        return  true;
                }
            }
        }
    }
    return false;
}

int main()
{
    int T,m,a,b,c,cas=0;
    scanf("%d",&T);
    while(T--)
    {
        cnt=0;
        memset(head,-1,sizeof(head));
        scanf("%d%d",&n,&m);
        int maxn=0;
        while(m--)
        {
            scanf("%d%d%d",&a,&b,&c);
            add(--a,--b,c+0.0);
            maxn=max(maxn,c);
        }
        printf("Case #%d: ",++cas);
        if(!judge(maxn+1.0)){
            printf("No cycle found.\n");
            continue;
        }
        double l=0.0,r=(double)maxn;
        while(r-l>1e-3){
            double m=l+(r-l)/2;
            if(judge(m))   r=m;
            else    l=m;
        }
        printf("%.2lf\n",l);
    }
    return 0;
}