poj 2031 Kruskal

//计算几何+最小生成树//注意精度//若两单元园心距离小与半径之和，则距离为0//反之，为距离-半径之和#include <iostream>#include <algorithm>#include <cstdio>#include <cmath>using namespace std;const int MAXN = 101;const int MAXM = 500000;int n;int M;double cost;double eps = 0.0000001;struct edge{int u;int v;double w;}edges[MAXM];struct unit{double x;double y;double z;double r;}units[MAXN];int cmp(const void *a,const void *b){edge aa = *(const edge *)a;edge bb = *(const edge *)b;return aa.w - bb.w;}int Father[MAXN];int Rank[MAXN];void Make_Set(){for(int i = 0; i < MAXN; i++){Father[i] = i;Rank[i] = 1;}}int Find(int x){while(x != Father[x])x = Father[x];return x;}void Union(int x,int y){x = Find(x);y = Find(y);if(x == y)return;if(Rank[x] > Rank[y]){Father[y] = x;Rank[x] += Rank[y];}else{Father[x] = y;Rank[y] += Rank[x];}}double distance(double x1,double y1,double z1,double x2,double y2,double z2){return sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)+(z2-z1)*(z2-z1));}void Kruskal(){int u,v;Make_Set();for(int i = 0; i < M; i++){u = Find(edges[i].u);v = Find(edges[i].v);if(u != v){cost += edges[i].w;Union(u,v);}}}int main(){while(cin>>n){if(n == 0)break;for(int i = 0; i < n; i++){cin>>units[i].x>>units[i].y>>units[i].z>>units[i].r;}M = 0;cost = 0;for(int i = 0; i < n-1; i++){for(int j = 1; j < n; j++ ){double dis = distance(units[i].x,units[i].y,units[i].z,units[j].x,units[j].y,units[j].z);edges[M].u = i;edges[M].v = j;if((dis - (units[i].r + units[j].r)) < eps){edges[M].w = 0;}else{edges[M].w = dis - (units[i].r + units[j].r);    //cout<<dis<<endl;}M++;}}qsort(edges,M,sizeof(edges[0]),cmp);Kruskal();printf("%.3f\n",cost);}return 0;}