bzoj1626 / P2872 [USACO07DEC]道路建设Building Roads

P2872 [USACO07DEC]道路建设Building Roads

kruskal求最小生成树。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<queue>
 #include<algorithm>
 #define re register
 using namespace std;
 typedef double ld;
 typedef long long ll;
 ll sqr(ll a){return a*a;}
 #define N 1002
 struct node{ll x,y;}a[N];
 struct edge{
     int f,t; ld dis;
     edge(){}
     edge(int A,int B,ld C):
         f(A),t(B),dis(C)
     {}
     bool operator < (const edge &tmp) const{return dis<tmp.dis;}
 }b[N*N];
 int n,m,tp,fa[N],k; ld ans;
 ld dist(node A,node B){return sqrt((ld)(sqr(A.x-B.x)+sqr(A.y-B.y)));}
 int find(int x){return fa[x]==x?x:fa[x]=find(fa[x]);}
 void uni(int x,int y){
     int r1=find(x),r2=find(y);
     if(r1!=r2) fa[r2]=r1;
 }
 int main(){
     scanf("%d%d",&n,&m); int q1,q2;
     for(re int i=;i<=n;++i){
         scanf("%lld%lld",&a[i].x,&a[i].y); fa[i]=i;
         for(re int j=;j<i;++j) b[++tp]=edge(j,i,dist(a[j],a[i]));//把可能的边存起来
     }sort(b+,b+tp+);
     for(re int i=;i<=m;++i){
         scanf("%d%d",&q1,&q2);
         if(find(q1)!=find(q2)) ++k,uni(q1,q2);
     }
     for(re int i=;i<=tp&&k<n-;++i)
         if(find(b[i].f)!=find(b[i].t)){
             uni(b[i].f,b[i].t);
             ans+=b[i].dis; ++k;
         }
     printf("%.2lf",ans);
     return ;
 }