[Explanations] luogu_P2502 [HAOI2006] travel (minimum spanning tree / disjoint-set fucks

Title means minimum given a map and s, t two points Q t s to the maximum path weight side / right minimum edge

In fact, it is to make maximum edge weight as small as possible, as large as the smallest edge weight

The right side-by-side sorting, enumeration biggest edge, in descending order smaller than join his side until the s and t Unicom, the smallest at this time the right side maximum, updated answers

Not too bzoj (shabi)

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int maxn=509;
const int maxm=5009;
int n,m,s,t;
struct node{
    int u,v,w;
    bool operator <(const node&t)const{
        return w<t.w;
    }
}e[maxm];
int fa[maxn];
int find(int x){
    while(x!=fa[x])x=fa[x]=fa[fa[x]];
    return x;
}
ll gcd(ll a,ll b){
    return b==0?a:gcd(b,a%b);
}
struct frac{
    long long up,dn;
    frac(){}
    frac(ll uu,ll dd){
        up=uu;dn=dd;
    }
    void set(){
        int g=gcd(up,dn);
        up/=g,dn/=g;
    }
    void out(){
//        set();
        if(dn==1)printf("%d\n",up);
        else printf("%d/%d\n",up,dn);
    }
    bool operator <(const frac&t)const{
        if(up*t.dn<dn*t.up)return 1;
        else return 0;
    }
}ans;
int vis[maxn];
int main(){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)fa[i]=i;
    for(int i=1,u,v;i<=m;i++){
        scanf("%d%d%d",&e[i].u,&e[i].v,&e[i].w);
        u=find(e[i].u),v=find(e[i].v);
        if(u!=v)fa[u]=v;
    }
    scanf("%d%d",&s,&t);
    if(find(s)!=find(t)){
        printf("IMPOSSIBLE");
        return 0;
    }
    int ff=find(s);
    for(int i=1;i<=n;i++)if(find(i)!=ff)vis[i]=1;
    for(int i=1;i<=n;i++)fa[i]=i;
    sort(e+1,e+1+m);
    ans=frac(1e8,1);
    for(int i=1;i<=m;i++){
        int u=e[i].u,v=e[i].v;
        if(vis[u] || vis[v])continue;
        for(int j=1;j<=n;j++)fa[j]=j;
        for(int j=i;j>=1;j--){
            int u=e[j].u,v=e[j].v;
            if(vis[u] || vis[v])continue;
            int uu=find(u),vv=find(v);
            if(uu!=vv){
                fa[uu]=vv;
                if(find(s)==find(t)){
                    frac a=frac(e[i].w,e[j].w);
                    a.set();
                    if(a<ans)ans=a;
                    break;
                }
            }
        } 
    }
    Years. set (); 
    years. out (); 
}