Shortest Summation Distance [NCTU Floor 9] [Bruteforce]

#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <sstream>
#include <cstdlib>
using namespace std;

struct Point{
    int x, y, index;
    Point(int x, int y, int idx){
        this->x = x;
        this->y = y;
        this->index = idx;
    }
};

void createCombinations(vector <int> arr, string out, int i, int n, int k, vector <string> &results){
    if(k == 0){
        results.push_back(out);
        return;
    }
    for(int j = i; j < n; j++){
        createCombinations(arr, out + " " + to_string(arr[j]), j + 1, n, k - 1, results);
    }
}

double calculateDistance(int x1, int y1, int x2, int y2){
    return sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
}

bool compareDistance(pair <Point, Point> p1, pair <Point, Point> p2){
    return calculateDistance(p1.first.x, p1.first.y, p1.second.x, p1.second.y) < calculateDistance(p2.first.x, p2.first.y, p2.second.x, p2.second.y);
}

void solve(vector <Point> houses){
    const int n = houses.size();
    vector <pair<Point, Point>> points;
    vector <double> distances;
    vector <bool> flag(n, false);
    vector <int> index(n * (n - 1) / 2);
    vector <string> combinations;

    for(int i = 0; i < index.size(); i++){
        index[i] = i;
    }
    createCombinations(index, "", 0, n * (n - 1) / 2, n / 2, combinations);

    for(int i = 0; i < n; i++){
        for(int j = i + 1; j < n; j++){
            points.push_back({houses[i], houses[j]});
        }
    }
    for(int i = 0; i < n * (n - 1) / 2; i++){
        distances.push_back(calculateDistance(points[i].first.x, points[i].first.y, points[i].second.x, points[i].second.y));
    }

    int pair;
    bool valid;
    double sum = 10e9, temp = 0;
    for(int i = 0; i < combinations.size(); i++){
        fill(flag.begin(), flag.end(), false);
        temp = 0;
        valid = true;
        stringstream ss(combinations[i]);
        while(ss >> pair){
            if(!flag[points[pair].first.index] && !flag[points[pair].second.index]){
                temp += distances[pair];
                flag[points[pair].first.index] = true;
                flag[points[pair].second.index] = true;
            }else{
                valid = false;
                break;
            }
        }
        if(valid){
            sum = min(sum, temp);
        }
        ss.clear();
    }
    cout << fixed << setprecision(2) << sum << " ";
}

int main(){
    int n, x, y, index;
    vector <Point> houses;
    string temp;
    getline(cin, temp);
    stringstream stream(temp);
    while(stream >> n){
        index = 0;
        houses.reserve(2 * n);
        for(int i = 0; i < 2 * n; i++){
            stream >> x >> y;
            Point p(x, y, index++);
            houses.push_back(p);
        }
        solve(houses);
        houses.clear();
    }
    return 0;
}