bzoj1821: [JSOI2010]Group 部落划分 Group

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
const int maxn = 1000 + 10;
const int maxm = 2000000 + 10;

struct Point {
    int x,y;
} a[maxn];

struct Edge {
    int u,v,w;
} g[maxm];

int n,k,res,eid;
int f[maxn];

int find(int x) {
    return f[x]==x?x:f[x]=find(f[x]);
}

int sqr(int x) {
    return x*x;
}

int foo(Point a,Point b) {
    return sqr(a.x-b.x)+sqr(a.y-b.y);    
}

void addedge(int a,int b,int c) {
    ++eid; g[eid].u=a; g[eid].v=b; g[eid].w=c;    
}

bool cmp(Edge a,Edge b) {
    return a.w<b.w;    
}

int main() {
    scanf("%d%d",&n,&k);
    for(int i=1;i<=n;i++) scanf("%d%d",&a[i].x,&a[i].y);
    for(int i=1;i<=n;i++)
    for(int j=i+1;j<=n;j++)
        addedge(i,j,foo(a[i],a[j]));
    sort(g+1,g+eid+1,cmp);
    
    for(int i=1;i<=n;i++) f[i]=i;
    for(res=1;res<=eid;res++) {
        int ru=find(g[res].u),rv=find(g[res].v);
        if(ru!=rv) {
            if(n>k) {
                f[ru]=rv;
                n--;    
            }
            else break;
        }
    }
    printf("%.2lf\n",sqrt(g[res].w));
    return 0;    
}