bzoj1050: [HAOI2006]旅行comf

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
#define rep(i,s,t) for(int i=s;i<=t;i++)
#define dwn(i,s,t) for(int i=s;i>=t;i--)
#define clr(x,c) memset(x,c,sizeof(x))
int read(){
    int x=0;char c=getchar();
    while(!isdigit(c)) c=getchar();
    while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();
    return x;
}
const int nmax=505;
const int maxn=5005;
const int inf=0x7f7f7f7f;
struct edge{
    int u,v,d;
    bool operator<(const edge&rhs) const{
      return d<rhs.d;}
};
edge es[maxn];
int fa[nmax];
int find(int x){
    return fa[x]==x?x:fa[x]=find(fa[x]);
}
int gcd(int a,int b){
    return b==0?a:gcd(b,a%b);
}
int main(){
    int n=read(),m=read();
    rep(i,1,m) es[i].u=read(),es[i].v=read(),es[i].d=read();
    sort(es+1,es+m+1);
    int ta,tb,s=read(),t=read(),aa,ab;double ans=30005;
    rep(i,1,m){ 
        if(es[i].d==es[i-1].d) continue;
        rep(j,1,n) fa[j]=j;
        rep(j,i,m){
            ta=find(es[j].u);tb=find(es[j].v);
            if(ta!=tb) fa[ta]=tb;
            else continue;
            if(find(s)==find(t)) {
                if(ans>es[j].d*1.0/es[i].d){
                    ans=es[j].d*1.0/es[i].d,aa=es[j].d,ab=es[i].d;
                }
                break;
            }
        }
    }
    //printf("%d %d %lf\n",aa,ab,ans);
    if(ans==30005) printf("IMPOSSIBLE\n");
    else if(aa%ab==0) printf("%d\n",aa/ab);
    else{
        int tmp=gcd(aa,ab);
        printf("%d/%d\n",aa/tmp,ab/tmp);
    }
    return 0;
}