【并查集】BZOJ1050 [HAOI2006]旅行comp

#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=505,maxe=5005;
int n,e,S,T,fa[maxn];
struct edge{
int x,y,w;
bool operator<(const edge&b)const{
return w<b.w;
}
}a[maxe];
inline int red(){
int tot=0;char ch=getchar();
while (ch<'0'||'9'<ch) ch=getchar();
while ('0'<=ch&&ch<='9') tot=tot*10+ch-48,ch=getchar();
return tot;
}
int getfa(int x){
return fa[x]==x?x:fa[x]=getfa(fa[x]);
}
void merge(int x,int y){
fa[getfa(x)]=getfa(y);
}
int gcd(int x,int y){
return y==0?x:gcd(y,x%y);
}
int main(){
n=red(),e=red();
for (int i=1;i<=e;i++) a[i].x=red(),a[i].y=red(),a[i].w=red();
S=red(),T=red();
sort(a+1,a+1+e);
int ansx=40000,ansy=1;
for (int i=e;i>=1;i--){
for (int j=1;j<=n;j++) fa[j]=j;
for (int j=i;j>=1;j--){
merge(a[j].x,a[j].y);
if (getfa(S)==getfa(T)){
if (a[i].w*ansy<a[j].w*ansx) ansx=a[i].w,ansy=a[j].w;
break;
}
}
}
int t=gcd(ansx,ansy);
ansx/=t;ansy/=t;
if (ansx==40000) printf("IMPOSSIBLE");else
if (ansy>1) printf("%d/%d",ansx,ansy);else printf("%d",ansx);
return 0;
}