可变长子网掩码划分例题_最小生成树是什么

输出格式
一个实数，表示最小的 d 值，结果保留 2 位小数。

数据范围
1≤n≤500,
0≤x,y≤104,
0≤k≤100
输入样例：
3 2
10 10
10 0
30 0
输出样例：
10.00

#include <iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
typedef pair<int,int>PII;
const int N = 1000;
#define x first
#define y second
int n,k;
const int M = N * N;
const double eps = 1e-6;
struct Edge{ 
   
    int u,v;
    double w;
    bool operator<(const Edge& a)const{ 
   
        return w < a.w;
    }
}edge[M];
    int cnt = 0;
double get_distance(int a,int b,int c,int d){ 
   
    return sqrt((a - c) * (a - c) + (b - d) * (b - d));
}
PII ver[N];
int f[N];
int Find(int x){ 
   
    return f[x] = (x == f[x] ? x : Find(f[x]));
}
int dcmp(double x,double y){ 
   
    if(abs(x - y) < eps)return 0;
    if(x < y)return -1;
    return 1;
}
bool check(double mid){ 
   
    int num = 0;
    for(int i = 0;i <= n;i ++)f[i] = i;
    for(int i = 0;i < cnt;i ++){ 
   
        double w = edge[i].w;
        if(dcmp(mid,w) == -1)continue;
        int a = Find(edge[i].u),b = Find(edge[i].v);
        if(a != b){ 
   
            f[a] = b;
            num ++;
        }
    }
    return n - num <= k;
}
int main(){ 
   
    cin>>n>>k;
    for(int i = 0;i < n;i ++){ 
   
        cin>>ver[i].x>>ver[i].y;
    }
    double l = 0,r = 0;
    for(int i = 0;i < n;i ++){ 
   
        for(int j = i + 1;j < n;j ++){ 
   
            edge[cnt].u = i,edge[cnt].v = j;
            edge[cnt].w = get_distance(ver[i].x,ver[i].y,ver[j].x,ver[j].y);
            r = max(r,edge[cnt].w);
            cnt ++;
        }
    }
    sort(edge,edge + cnt);
    while(abs(l - r) > eps){ 
   
        double mid = (l + r) / 2;
        if(check(mid))r = mid;
        else l = mid;
    }
    printf("%.2f\n",l);
    return 0;
}