4002

4002

Problem B

Time Limit : 2000/1000ms (Java/Other)   Memory Limit : 65536/32768K (Java/Other)

Total Submission(s) : 58   Accepted Submission(s) : 18

Problem Description

Eddy begins to like painting pictures recently ,he is sure of himself to become a painter.Every day Eddy draws pictures in his small room, and he usually puts out his newest pictures to let his friends appreciate. but the result it can be imagined, the friends are not interested in his picture.Eddy feels very puzzled,in order to change all friends 's view to his technical of painting pictures ,so Eddy creates a problem for the his friends of you.<br>Problem descriptions as follows: Given you some coordinates pionts on a drawing paper, every point links with the ink with the straight line, causes all points finally to link in the same place. How many distants does your duty discover the shortest length which the ink draws?<br>

 

Input

The first line contains 0 < n <= 100, the number of point. For each point, a line follows; each following line contains two real numbers indicating the (x,y) coordinates of the point. <br><br>Input contains multiple test cases. Process to the end of file.<br>

 

Output

Your program prints a single real number to two decimal places: the minimum total length of ink lines that can connect all the points. <br>

 

Sample Input

31.0 1.02.0 2.02.0 4.0

 

Sample Output

3.41

 

题意：用最短的连线把所有的点连起来；


思路：大方向很好想，最小生成树+并查集；
      但是代码实现很困难。
      在网上找到了别人的代码。参考着写的。
      初始化的时候把边初始化为了0，出了很多问题；
AC代码：
#include <stdio.h>
#include <iostream>
#include <string.h>
#include <algorithm>
#include <math.h>
using namespace std;


const int N = 105;
struct Point {
    double x,y;
}p[N];
struct Edge{
    int s,e;
    double len;
}edge[N*(N-1)/2];
int father[N],n;
double dis(Point a,Point b){
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
int _find(int x){
    if(x==father[x]) return x;
    return _find(father[x]);
}
int cmp(Edge a,Edge b){
    return a.len<b.len;
}
double kruskal(int m){
    sort(edge+1,edge+m+1,cmp);
    double cost=0;
    for(int i=1;i<=m;i++){
        int x = _find(edge[i].s);
        int y = _find(edge[i].e);
        if(x!=y){
            father[x] = y;
            cost +=edge[i].len;
        }
    }
    return cost;
}
int main(){
    while(scanf("%d",&n)!=EOF){
        for(int i=0;i<n;i++) father[i] = i;
        for(int i=0;i<n;i++){
            scanf("%lf%lf",&p[i].x,&p[i].y);
        }
        int m =1; ///边的数量
        for(int i=0;i<n;i++){
            for(int j=i+1;j<n;j++){ ///这里是i+1开始,从0开始会多出很多边
                edge[m].s =i;
                edge[m].e = j;
                edge[m++].len = dis(p[i],p[j]);
            }
        }
        m--; ///记得
        printf("%.2lf\n",kruskal(m));
    }
}