[USACO14MAR]浇地Watering the Fields

 1 // luogu-judger-enable-o2
 2 #include <cstdio>
 3 #include <cmath>
 4 #include <algorithm>
 5 using namespace std;
 6 int n,c,cnt;
 7 int ans;
 8 int x[2005],y[2005],fa[2005];
 9 struct Node{
10     int x;
11     int y;
12     int dis;
13 }a[4000005];
14 inline int Find(int i){
15     if(fa[i]==i)return i;
16     return fa[i]=Find(fa[i]);
17 }
18 inline void Union(int x,int y){
19     int f1=Find(x);
20     int f2=Find(y);
21     if(f1!=f2)fa[f1]=f2;
22     return;
23 }
24 inline bool cmp(Node a,Node b){
25     if(a.dis==b.dis)return a.x<b.x;
26     return a.dis<b.dis;
27 }
28 int main(){
29     scanf("%d%d",&n,&c);
30     for(register int i=1;i<=n;i++)
31         fa[i]=i;
32     for(register int i=1;i<=n;i++)
33         scanf("%d%d",&x[i],&y[i]);
34     for(register int i=1;i<=n;i++)
35         for(register int j=i+1;j<=n;j++){
36             if((x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j])>=c){
37                 a[++cnt].x=i;
38                 a[cnt].y=j;
39                 a[cnt].dis=(x[i]-x[j])*(x[i]-x[j])+(y[i]-y[j])*(y[i]-y[j]);
40             }
41         }
42     int k=0;
43     sort(a+1,a+cnt+1,cmp);
44     for(register int i=1;i<=cnt;i++){
45         if(Find(a[i].x)!=Find(a[i].y)){
46             Union(a[i].x,a[i].y);
47             ans+=a[i].dis;
48             k++;
49         }
50         if(k==n-1)break;
51     }
52     if(k==n-1&&ans>=c)printf("%d\n",ans);
53     else printf("-1\n");
54     return 0;
55 }