71 lines
1.4 KiB
C++
71 lines
1.4 KiB
C++
#include"stdio.h"
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#include"string.h"
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#include"stdlib.h"
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#include"math.h"
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int pre[100];
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struct A
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{
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int a,b,len;
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}eage[3000];
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int k;
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int x[100],y[100];
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void build(int n)
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{
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int i;
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for(i=0;i<n;i++) pre[i]=i;
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}
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int find(int k)
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{
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if(pre[k]==k) return k;
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pre[k]=find(pre[k]);
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return pre[k];
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}
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void Union(int f1,int f2)
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{
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pre[f1]=f2;
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}
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int cmp(const void *a,const void *b)
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{
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struct A *c,*d;
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c=(struct A *)a;
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d=(struct A *)b;
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return c->len-d->len;
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}
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int main()
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{
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int n;
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int i,l;
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int d1,d2;
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int f1,f2;
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double ans;
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while(scanf("%d",&n),n)
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{
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build(n);
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scanf("%d%d",&d1,&d2);
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d1--;d2--;
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for(i=0;i<n;i++) scanf("%d%d",&x[i],&y[i]);
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k=0;
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for(i=1;i<n;i++)
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for(l=0;l<i;l++)
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{
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eage[k].a=i;
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eage[k].b=l;
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eage[k].len=(x[i]-x[l])*(x[i]-x[l])+(y[i]-y[l])*(y[i]-y[l]);
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k++;
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}
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qsort(eage,k,sizeof(eage[0]),cmp);
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ans=sqrt((double)(x[d1]-x[d2])*(x[d1]-x[d2])+(y[d1]-y[d2])*(y[d1]-y[d2]));
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Union(d1,d2);
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for(i=0;i<k;i++)
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{
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f1=find(eage[i].a);
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f2=find(eage[i].b);
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if(f1==f2) continue;
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Union(f1,f2);
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ans+=sqrt((double)eage[i].len);
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}
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printf("%.2lf\n",ans);
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}
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return 0;
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}
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