55 lines
839 B
C++
55 lines
839 B
C++
#include<cstdio>
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#include<algorithm>
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using namespace std;
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const int maxn=100;
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struct Edge
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{
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int a,b,v;
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};
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inline bool operator<(const Edge& a,const Edge& b)
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{
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return a.v<b.v;
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}
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Edge e[maxn*maxn+5];
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int fa[maxn+5];
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const int oo=1<<30;
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int ff(int n)
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{
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int a=n,b;
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while(n!=fa[n]) n=fa[n];
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while(a!=n)
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{
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b=fa[a];
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fa[a]=n;
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a=b;
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}
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return n;
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}
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int n,m,res,L,R,cnt;
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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while(scanf("%d%d",&n,&m)==2&&n)
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{
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for(int i=0;i<m;i++) scanf("%d%d%d",&e[i].a,&e[i].b,&e[i].v);
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sort(e,e+m);
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res=oo;
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for(L=0;L<m;L++)
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{
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for(int i=1;i<=n;i++) fa[i]=i;
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cnt=n;
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for(R=L;cnt>1&&R<m;R++)
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if(ff(e[R].a)!=ff(e[R].b))
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{
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fa[ff(e[R].b)]=ff(e[R].a);
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cnt--;
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}
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if(cnt==1) res=min(res,e[R-1].v-e[L].v);
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}
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printf("%d\n",res==oo?-1:res);
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}
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return 0;
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}
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