Highways POJ - 1751

题目链接：https://vjudge.net/problem/POJ-1751

思路：

最小生成树板子，只需要多记录每个dis[x]的权值是从哪个点到x这个点的。

 #include <stdio.h>
 #include <iostream>
 #include <queue>
 #include <math.h>
 #include <algorithm>
 using namespace std;

 const int N = (int)1e3 + ;
 const int inf = (int)1e9;
 double px[N];
 double py[N];
 double g[N][N];
 bool vis[N];
 int n,m;
 int s;

 struct info{
     int from;
     double w;
 }dis[N];

 struct node{
     int loc;
     double w;
     bool friend operator<(const node & a,const node& b){
         return a.w > b.w;
     }
 };
 priority_queue<node > que;

 inline double dist(int a,int b){
     return sqrt((px[a]-px[b])*(px[a]-px[b])+(py[a]-py[b])*(py[a]-py[b]));
 }

 void build_map(){

     for(int i = ; i <= n; i++)
         for(int j = i + ; j <= n; j++)
             g[i][j] = g[j][i] = dist(i,j);

     for(int i = ; i <= n; i++) g[i][i] = ;
 }

 void prime(){

     for(int i = ; i <= n; i++){
         vis[i] = ;
         dis[i].w = inf;
     }

     if(!s) s = ;

     que.push(node{s,});
     dis[s].from = ;
     dis[s].w = ;

     while(!que.empty()){
         int u = que.top().loc;
         que.pop();
         vis[u] = ;

         for(int v = ; v <= n; v++){
             if(!vis[v] && dis[v].w > g[u][v]){
                 dis[v].w = g[u][v];
                 dis[v].from = u;
                 que.push(node{v,dis[v].w});
             }
         }
     }

     for(int i = ; i <= n; i++){
         if(dis[i].w == ) continue;
         printf("%d %d\n",dis[i].from,i);
     }
 }

 int main(){

     scanf("%d",&n);

     for(int i = ; i <= n; i++)
         scanf("%lf%lf",&px[i],&py[i]);

     build_map();

     scanf("%d",&m);
     int u,v;

     for(int i = ; i <= m ;i++){
         scanf("%d%d",&u,&v);
         s = u;
         g[u][v] = g[v][u] = ;
     }

     prime();
     return ;
 }