题解 | #Freckles#

#include<cmath>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

struct point{
    float x,y;
    int loc;
    bool operator==(const point &p)
    {
        return (this->x == p.x) && (this->y == p.y);
    }
}p;

struct dist{
    float dis;
    point id;

};

float dis(point a,point b){
    return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}

bool cmp(dist a,dist b){
    return a.dis<b.dis;
}

int main() {
    int c ;
    float res=0,a,b;
    cin>>c;
    vector<point> aa,bb;
    for (int i=0;i<c;i++){
        point s;
        cin>>s.x>>s.y;
        aa.push_back(s);
    }
    bb.push_back(aa[0]);
    aa.erase(aa.begin());
    vector<dist> di;
    while(aa.size()!=0){
        int m=0;
        for(int i=0;i<aa.size();i++){
            for(int j=0;j<bb.size();j++){
                dist dd;
                dd.dis=dis(aa[i],bb[j]);dd.id=aa[i];
                di.push_back(dd);
                m++;
            }
        }
        sort(di.begin(),di.begin()+m,cmp);
        res +=(*di.begin()).dis;
        dist p=di[0];
        bb.insert(bb.begin(),p.id);
        for(vector<point>::iterator it=aa.begin();it!=aa.end();){
            if(*it==p.id){aa.erase(it);}
            else{it++;}
        }
        di.clear();

    }
    printf("%.2f", res);
}