poj2349

求生成树中s-1短的边。网上说可以用prim算法，我用的是kruskal算法，时间真的惨不忍睹，我怀疑prim会超时。

#include<iostream>#include<algorithm>#include<stdlib.h>#include<string.h>#include<math.h>#include<string>#include<vector>#include<queue>#include<list>using namespace std;typedef long long lld;typedef unsigned int ud;#define Inf INT_MAX//int最大#define Min(x,y) (x)<(y)?(x):(y)#define Max(x,y) (x)>(y)?(x):(y)#define PQ priority_queue#define Q queue#define N 505struct Edge{int u,v;double w;}edge[N*(N-1)/2];int S,P,m;struct Vex{double x,y;}vex[N];int parent[N];double mst_w[N];void InitParent(){for(int i=0;i<P;i++)parent[i]=-1;}int find(int x){return parent[x]<0 ? x : find(parent[x]);}void merge(int r1,int r2){if(parent[r1]>parent[r2]){parent[r1]=r2;parent[r2]-=parent[r1];}else{parent[r2]=r1;parent[r1]-=parent[r2];}}bool cmp(Edge e1,Edge e2){return e1.w<e2.w;}double Kruskal(){sort(edge,edge+m,cmp);InitParent();int k=0;for(int i=0;i<m;i++){int u=find(edge[i].u);int v=find(edge[i].v);if(u!=v){mst_w[k++]=edge[i].w;merge(u,v);if(k==P-1)break;}}return mst_w[k-S];}double GetW(Vex v1,Vex v2){return sqrt((v1.x-v2.x)*(v1.x-v2.x)+(v1.y-v2.y)*(v1.y-v2.y));}int main(){int T;scanf("%d",&T);while(T--){scanf("%d%d",&S,&P);for(int i=0;i<P;i++)scanf("%lf%lf",&vex[i].x,&vex[i].y);m=0;for(int i=0;i<P;i++)for(int j=i;j<P;j++){if(i==j)continue;edge[m].u=i;edge[m].v=j;edge[m++].w=GetW(vex[i],vex[j]);}printf("%.2lf\n",Kruskal());}return 0;}