最小生成树

Kruskal

#include<cmath>
#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;

struct A{
    int x,y;
    double z;
}a[500010];
int r[755];
int find_(int x)
{
    while(x!=r[x])
        x=r[x];
    return x;
}

int cmp(A a,A b)
{
    return a.z<b.z;
}
int main()
{
    int n,m,i,j,k,c,b,x[755],y[755];
    while(scanf("%d",&n)!=EOF)
    {
        for(i=1;i<=n;i++)
            scanf("%d%d",&x[i],&y[i]);
        for(i=1;i<=n;i++)
            r[i]=i;
        k=0;
        for(i=1;i<=n;i++)
            for(j=1;j<=n;j++){
                if(i>j){
                    double s=sqrt(  (x[i]-x[j])*(x[i]-x[j])+ (y[i]-y[j])*(y[i]-y[j]) );
                    a[++k].x=i;
                    a[k].y=j;
                    a[k].z=s;
                }
            }
        scanf("%d",&m);
        while(m--){
            scanf("%d%d",&c,&b);
            int aa=find_(c);
            int bb=find_(b);
            if(aa!=bb){
                r[aa]=bb;
            }
        }

        sort(a+1,a+1+k,cmp);
        double ans=0;
        for(i=1;i<=k;i++)
        {
            int aa=find_(a[i].x);
            int bb=find_(a[i].y);
            if(aa!=bb){
                r[aa]=bb;
                ans=ans+a[i].z;
            }
        }
        printf("%.2lf\n",ans);


    }
    return 0;
}

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