P2502 [HAOI2006]鏃呰 鏈€灏忕敓鎴愭爲

Posted 2022-04-28

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鎬濊矾锛氭灇涓捐竟闆嗭紝鏈€灏忕敓鎴愭爲

鎻愪氦锛?娆?/p>

棰樿В锛氾紙濡傛€濊矾锛?/p>

#include<cstdio>
#include<iostream>
#include<algorithm>
#define R register int
using namespace std;
#define ull unsigned long long
#define ll long long
#define pause (for(R i=1;i<=10000000000;++i))
#define In freopen("NOIPAK++.in","r",stdin)
#define Out freopen("out.out","w",stdout)
namespace Fread 
static char B[1<<15],*S=B,*D=B;
#ifndef JACK
#define getchar() (S==D&&(D=(S=B)+fread(B,1,1<<15,stdin),S==D)?EOF:*S++)
#endif
inline int g() 
    R ret=0,fix=1; register char ch; while(!isdigit(ch=getchar())) fix=ch==鈥?/span>-鈥?/span>?-1:fix;
    if(ch==EOF) return EOF; do ret=ret*10+(ch^48); while(isdigit(ch=getchar())); return ret*fix;
 inline bool isempty(const char& ch) return (ch<=36||ch>=127);
inline void gs(char* s) 
    register char ch; while(isempty(ch=getchar()));
    do *s++=ch; while(!isempty(ch=getchar()));

 using Fread::g; using Fread::gs;

namespace Luitaryi 
const int N=510,M=5010;
int n,m,s,t,up,dn;
double anss=1E+9;
int fa[N];
struct edge  int u,v,w;
    inline bool operator < (const edge& that) constreturn w<that.w;
e[M];
inline int getf(int x) return x==fa[x]?x:fa[x]=getf(fa[x]);
inline void main() 
    n=g(),m=g();
    for(R i=1;i<=m;++i) e[i].u=g(),e[i].v=g(),e[i].w=g();
    sort(e+1,e+m+1); s=g(),t=g();
    for(R i=1;i<=m;++i)  R ans=0;//鏋氫妇涓嬬晫锛屾渶灏忕殑杈?
        for(R j=1;j<=n;++j) fa[j]=j;
        for(R j=i;j<=m;++j) //寰€涓婃灇涓撅紝鐩村埌涓ょ偣杩為€?
            R uf=getf(e[j].u),vf=getf(e[j].v);
            fa[uf]=vf;
            if(getf(s)==getf(t)) ans=j; break;
         if(i==1&&ans==0) return (void)printf("IMPOSSIBLE\n");
        if(ans==0) break; register double tmp=1.0*e[ans].w/e[i].w;
        if(tmp<anss) anss=tmp,up=e[ans].w,dn=e[i].w;
     R tmp=__gcd(up,dn); if(tmp==dn) printf("%d\n",up/dn);
    else printf("%d/%d\n",up/tmp,dn/tmp);


signed main() 
    Luitaryi::main();
    return 0;
 

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2019.07.20