ProgramAlgTrain/20240917/P1991/P1991.cpp

// #include <algorithm>
// #include <cmath>
// #include <iomanip>
// #include <ios>
// #include <iostream>
// #include <istream>
#include<bits/stdc++.h>

const int MAX_P = 500+5;

struct Dir{
    int x,y;
};

struct Edge{
    int s,e;
    double dis;
    bool operator<(const Edge that)const {
        return this->dis < that.dis;
    }
}edges[MAX_P*MAX_P];


int s,p;
Dir dirs[MAX_P];

decltype(Edge::dis) square(const decltype(Edge::dis) &n){
    return n*n;
}

int check_sets[MAX_P];

int find_set(const int n){
    if(check_sets[n]==n){
        return n;
    }else{
        check_sets[n] = find_set(check_sets[n]);
    }
    return check_sets[n];
}

void merge_set(const int a,const int b){
    check_sets[find_set(a)] = check_sets[find_set(b)];
}

int main(){
    std::cin.sync_with_stdio(false),std::cin.tie(0),std::cout.tie(0);

    std::cin>>s>>p;

    for(int i=1;i<=p;i++){
        check_sets[i]=i;
    }

    for(int i=1;i<=p;i++){
        std::cin>>dirs[i].x>>dirs[i].y;
    }

    int flag = -1;
    for(int i=1;i<=p;i++){
        for(int j=i+1;j<=p;j++){
            flag++;
            edges[flag].e=i,edges[flag].s=j,edges[flag].dis=std::sqrt(square(dirs[i].x-dirs[j].x)+square(dirs[i].y-dirs[j].y));
        }
    }

    std::sort(edges,edges+flag+1);

    decltype(Edge::dis) ans{0};

    // #define NV(v)std::cout<<#v<<" : "<<(v)<<"\n";
    #define NV(v)

    int cnt{0};

    for(int i=0;i<flag;i++){
        NV(find_set(edges[i].e));
        NV(find_set(edges[i].s));

        if(find_set(edges[i].e)!=find_set(edges[i].s)){
            NV(edges[i].dis)
            merge_set(edges[i].e,edges[i].s);
            // std::cout<<"merge "<<edges[i].e<<" "<<edges[i].s<<"\n";
            ans=edges[i].dis;
            cnt++;
            if(cnt>=p-s){
                std::cout<<std::fixed<<std::setprecision(2)<<ans<<"\n";
                return 0;
            }   
        }
    }
}