01分数规划

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxm 3005
#define maxe 20005
#define eps 1e-10
using namespace std;
int n,point[maxm]={0},next[maxe]={0},en[maxe]={0},tot=0;
double va[maxe],vv[maxe]={0},dis[maxm];
bool visit[maxm],flag;
int cmp(double x,double y){
    if (x-y>eps) return 1;
    if (y-x>eps) return -1;
    return 0;
}
void add(int u,int v,double w){
    next[++tot]=point[u];point[u]=tot;en[tot]=v;vv[tot]=w;
}
void spfa(int u){
    int i,j,v;visit[u]=true;
    for (i=point[u];i;i=next[i]){
        if (dis[v=en[i]]>dis[u]+va[i]){
            if (visit[v]){flag=true;break;}
            else{
                dis[v]=dis[u]+va[i];spfa(v);
            }
        }
    }visit[u]=false;
}
bool judge(double x){
    int i,j;flag=false;
    memset(dis,0,sizeof(dis));
    memset(visit,false,sizeof(visit));
    for (i=1;i<=tot;++i) va[i]=vv[i]-x;
    for (i=1;i<=n;++i){
        spfa(i);if (flag) return true;
    }return false;
}
int main(){
    int i,j,m,u,v;double w,l=0.0,r=0.0,mid;
    scanf("%d%d",&n,&m);
    for (i=1;i<=m;++i){
        scanf("%d%d%lf",&u,&v,&w);
        add(u,v,w*1.0);r=max(r,w*1.0);l=min(l,w*1.0);
    }while(cmp(l,r)<0){
        mid=(l+r)/2;
        if (judge(mid))r=mid;
        else l=mid;
    }printf("%.8f\n",l);
}