Building a Space Station POJ - 2031

Posted 2020-11-30 ssummerzzz

题目链接：https://vjudge.net/problem/POJ-2031

思路：最小生成树板子题

  1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <algorithm>
  5 #include <queue>
  6 #include <stack>
  7 #include <string>
  8 #include <map>
  9 #include <cmath>
 10 using namespace std;
 11  
 12 typedef long long LL;
 13 #define inf 1e11
 14 #define rep(i,j,k) for(int i = (j); i <= (k); i++)
 15 #define rep__(i,j,k) for(int i = (j); i < (k); i++)
 16 #define per(i,j,k) for(int i = (j); i >= (k); i--)
 17 #define per__(i,j,k) for(int i = (j); i > (k); i--)
 18 
 19 const int N = 110;
 20 int head[N];
 21 int cnt;
 22 double dis[N];
 23 bool vis[N];
 24 int n;
 25 
 26 struct Point{
 27     double x,y,z,r;
 28 }p[N];
 29 
 30 struct Edge{
 31     int to;
 32     double w;
 33     int nxt;
 34 }e[N*N];
 35 
 36 struct node{
 37     int u;
 38     double w;
 39     friend bool operator<(const node& a,const node& b){
 40         return a.w > b.w;
 41     }
 42 };
 43 
 44 priority_queue<node > que;
 45 
 46 void add(int u,int v,double w){
 47     e[cnt].to = v;
 48     e[cnt].w = w;
 49     e[cnt].nxt = head[u];
 50     head[u] = cnt++;
 51 }
 52 
 53 inline double get_dis(Point& a,Point& b){
 54     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)+(a.z-b.z)*(a.z-b.z))-a.r-b.r;
 55 }
 56 
 57 double prime(){
 58     while(!que.empty()) que.pop();
 59 
 60     rep(i,1,n){
 61         vis[i] = false;
 62         dis[i] = inf;
 63     }
 64     dis[1] = 0;
 65     que.push(node{1,dis[1]});
 66    
 67     int u,v;
 68     double w;
 69     while(!que.empty()){
 70         u = que.top().u;
 71         que.pop();
 72         if(vis[u]) continue;
 73         vis[u] = true;
 74 
 75         for(int o = head[u]; ~o; o = e[o].nxt){
 76             v = e[o].to;
 77             w = e[o].w;
 78 
 79             if(!vis[v] && dis[v] > w){
 80                 dis[v] = w;
 81                 que.push(node{v,dis[v]});
 82             }
 83         }
 84     }
 85 
 86     double ans = 0;
 87     rep(i,1,n) ans += dis[i];
 88     return ans;
 89 }
 90 
 91 int main(){
 92 
 93     double tmp;
 94     while(~scanf("%d",&n)){
 95         if(n == 0) break;
 96         rep(i,1,n) head[i] = -1;
 97         cnt = 0;
 98 
 99         rep(i,1,n) scanf("%lf%lf%lf%lf",&p[i].x,&p[i].y,&p[i].z,&p[i].r);
100 //        rep(i,1,n) printf("%.3f %.3f %.3f %.3f
",p[i].x,p[i].y,p[i].z,p[i].r);
101 
102         rep(i,1,n) rep(j,i+1,n){
103             tmp = get_dis(p[i],p[j]);
104             add(i,j,tmp > 0 ? tmp : 0);
105             add(j,i,tmp > 0 ? tmp : 0);
106         }
107 
108         printf("%.3f
",prime());
109     }
110 
111     getchar(); getchar();
112     return 0;
113 }