sfa

Posted 2022-11-15 lamboofhome

#include <bits/stdc++.h>
#define M 100005
#define INF 100000;
using namespace std;
int x,y,i,cent,n,fa[M],que[M],t,ii,ans,a,s,m,j,nn,mins,vis;
struct edge
    int u;
    int v;
    int w;
  bool operator <(const edge &t)const 
  
      return w<t.w;
  
es[M];
int findloot(int kk)
  
    while(fa[kk]!=0)  que[++t]=kk,kk=fa[kk];
    while(t>0) fa[que[t--]]=kk;
    return kk;

void lianhe(int a,int b)

    int l=findloot(a);
    int r=findloot(b);
    if(l!=r)
    fa[l]=r;

int main()
    while(~scanf("%d%d",&n,&m))
    
        if(n==0&&m==0)
         break; 
       ans=INF;vis=0;cent=0;
       memset(es,0,sizeof(es)); 
     for(i=1;i<=m;i++)
     
      scanf("%d%d%d",&x,&y,&a);     
      es[cent].u=x,es[cent].v=y,es[cent++].w=a;
     
     sort(es,es+cent-1);
     for(j=0;j<cent;j++)
         
           memset(fa,0,sizeof(fa));
         mins=es[j].w;
        nn=n;
           for(i=j;i<cent;i++)
              
            if(findloot(es[i].u)!=findloot(es[i].v))
                lianhe(es[i].u,es[i].v); 
                    nn--;
            
            if(nn==1)
              vis=1;
                  ans=min(ans,es[i].w-mins);
            break;//zhiyi
            
        
    
    if(vis==1)
     printf("%d\n",&ans);
     else
     cout<<-1;