P2212Watering the Fields S（生成树）C++

P2212 [USACO14MAR]Watering the Fields S

输入：

3 11
0 2
5 0
4 3

输出：

46

Kruskal

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <vector>
#include <queue>
#include <cctype>
#define ri register int 
#define ll long long 
using namespace std;
const int maxn=2005;
const int inf=192681792;
struct Edge{
    
    
	int u,v,dis;
	bool operator <(const Edge& b)const{
    
    
		return dis<b.dis;
	}
}edge[19260817];//边数不要设小了 
int n,c,tot=0;
int px[maxn],py[maxn];
int fa[maxn];
int get(int x){
    
    
	if(fa[x]!=x)fa[x]=get(fa[x]);
	return fa[x];
}
inline void kruskal(){
    
    
	int u,v,dis;
	int cnt=0,ans=0;
	for(ri i=1;i<=n;i++){
    
    
		fa[i]=i;
	}
	for(ri i=1;i<=tot;i++){
    
    
		u=edge[i].u,v=edge[i].v;
		u=get(u),v=get(v);
		if(u!=v){
    
    
			fa[u]=v;
			ans+=edge[i].dis;
			cnt++;
	    }
	    if(cnt==n-1)break;
	}
	if(cnt==n-1)printf("%d",ans);
	else puts("-1");
	return ;
}
int main(){
    
    
	scanf("%d %d",&n,&c);
	for(ri i=1;i<=n;i++){
    
    
		scanf("%d %d",&px[i],&py[i]);
		for(ri j=1;j<i;j++){
    
    
			int d=(px[i]-px[j])*(px[i]-px[j])+(py[i]-py[j])*(py[i]-py[j]);
			if(d>=c){
    
    
				edge[++tot].u=i,edge[tot].v=j,edge[tot].dis=d;
			}
		}
	}
	sort(edge+1,edge+1+tot);
	kruskal();
	return 0;
}