BZOJ 1050 枚举+并查集

思路：

枚举最大边 像Kruskal一样加边 每回更新一下 就搞定了…

//By SiriusRen
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define N 10050
int n,m,s,t,fx,fy,f[N],stk[N],top,vis[N],recx,recy;
double ans=666666.0;
struct Node{int x,y,z;}node[N];
int find(int x){return x==f[x]?x:f[x]=find(f[x]);}
int gcd(int a,int b){return b?gcd(b,a%b):a;}
bool cmp(Node a,Node b){return a.z<b.z;}
int main(){
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)f[i]=i;
    for(int i=1;i<=m;i++){
        scanf("%d%d%d",&node[i].x,&node[i].y,&node[i].z);
        fx=find(node[i].x),fy=find(node[i].y);
        if(fx!=fy)f[fx]=fy;
    }
    scanf("%d%d",&s,&t);
    if(find(s)!=find(t)){puts("IMPOSSIBLE");return 0;}
    sort(node+1,node+1+m,cmp);
    for(int i=1;i<=m;i++){
        for(int j=1;j<=n;j++)f[j]=j;
        for(int j=i;j;j--){
            fx=find(node[j].x),fy=find(node[j].y);
            if(fx!=fy)f[fx]=fy;
            if(find(s)==find(t)){
                if(ans>1.0*node[i].z/node[j].z){
                    ans=1.0*node[i].z/node[j].z;
                    recx=node[i].z,recy=node[j].z;
                }
                break;
            }
        }
    }
    int GCD=gcd(recx,recy);
    if(GCD!=recy)printf("%d/%d",recx/GCD,recy/GCD);
    else printf("%d\n",recx/recy);
}