Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

C++: #include <cassert>

#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
// #include <boost/foreach.hpp>
// #include <boost/range/algorithm.hpp>
#define rep(i,j,k) for(int i=(int)j;i<(int)k;i++)
#define ll long long
#define Sort(v) sort(all(v))
//#define INF 1e9
#define LINF 1e18
#define END return 0
#define pb push_back
#define se second
#define fi first
#define pb push_back
#define all(v) (v).begin() , (v).end()
#define MP make_pair
#define int long long
using namespace std;
int day[12]={31,28,31,30,31,30,31,31,30,31,30,31};
// int dx[]={0,1,0,-1};
// int dy[]={1,0,-1,0};
struct edge{int to,cost;};
//typedef pair<int,int> P;

const long long MOD=1000000007LL;
bool isupper(char c){if('A'<=c&&c<='Z')return 1;return 0;}
bool islower(char c){if('a'<=c&&c<='z')return 1;return 0;}
bool isPrime(int x){if(x==1)return 0;if(x==2)return 1;if(x%2==0)return 0;for(int i=3;i*i<=x;i++)if(x%i==0)return 0;return 1;}
bool iskaibun(string s){for(int i=0;i<s.size()/2;i++)if(s[i]!=s[s.size()-i-1])return 0;return 1;}
bool isnumber(char c){return ('0'<=c&&c<='9');}
bool isalpha(char c){return (isupper(c)||islower(c));}
template<typename T> 
void print(vector<T> v){
    for(int i=0;i<v.size();i++){
        if(i)cout<<" ";
        cout<<v[i];
    }
    cout<<endl;
}
int INF=1e18;

template<typename T>
void printendl(vector<T> v){
    for(auto date:v)cout<<date<<endl;
}

template<typename T>
void printvv(vector<vector<T>> v){
    for(int i=0;i<v.size();i++){
        for(int j=0;j<v[i].size();j++){
            if(j)cout<<" ";
            cout<<v[i][j];
        }
        cout<<endl;
    }
}
int gcd(int a,int b){
    if(a<b)swap(a,b);
    if(b==0)return a;
    else return gcd(b,a%b);
}

struct Edge{
    int to,cost;
};

int prim(vector<vector<Edge>>& g, int n){
    typedef pair<int,int> P;
    vector<bool> used(n+1,false);
    int ret=0;
    priority_queue<P, vector<P>, greater<P>> que;
    que.push(P(0, 0)); //(コスト, 頂点)
    while(!que.empty()){
        P p=que.top();
        que.pop();
        if(used[p.second])continue;
        used[p.second]=true;
        ret+=p.first;
        for(int i=0;i<g[p.second].size();i++){
            Edge e=g[p.second][i];
            que.push(P(e.cost, e.to));
        }
    }
    return ret;
}

signed main (){
    int n;
    cin>>n;
    vector<vector<Edge>> v(n,vector<Edge>(0));
    rep(i,0,n){
        rep(j,0,n){
            int x;
            cin>>x;
            if(x!=-1){
                v[i].push_back(Edge{j,x});
            }
        }
    }
    cout<<prim(v,n)<<endl;

}
/*

*/

C++: #include<iostream>
#include<algorithm>
#define MAX 101
#define INF 1<<21
#define NIL -1
using namespace std;
int n,A[MAX][MAX];
int Minimum_Spanning_Tree(void){
    int color[MAX],d[MAX],vertices,mincost;
    for(int i=0;i<n;i++){
        color[i] = 0;
        d[i] = INF;
    }
    d[0] = 0;
    while(true){
        mincost = INF;
        vertices = NIL;
        for(int i=0;i<n;i++){
            if(color[i]!=1 & d[i]<mincost){
                mincost = d[i];
                vertices = i; 
            }
        }
        if(vertices == NIL){
            break;
        }
        color[vertices] = 1; 
        for(int i=0;i<n;i++){
            if(color[i]!=1 && A[vertices][i] != INF){
                if(A[vertices][i] < d[i]){
                    d[i] = A[vertices][i];
                }
            }
        }
    }
    int sum = 0;
    for(int i=0;i<n;i++){
        sum += d[i];
    }
    return sum;
}
int main(void){
    cin >> n;
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            cin >> A[i][j];
            if(A[i][j] == NIL){
                A[i][j] = INF;
            }
        }
    }
    cout << Minimum_Spanning_Tree() << endl;
    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
struct UnionFind{
    vector<int> parent;

    UnionFind(int n) : parent(n){
        for (int i = 0; i < n; i++)parent[i] = i;
    }

    int find(int e){
        if (parent[e] == e) return e;
        else return parent[e] = find(parent[e]);
    }

    void unite (int a, int b) {
        a = find(a);
        b = find(b);
        if (a == b) return;
        parent[a] = b;
    }

    bool same(int a, int b){
        return find(a) == find(b);
    }
};

int main() {
    vector<tuple<int, int, int>> a;
    int n, t, ans = 0;
    cin >> n;
    UnionFind uf(n);
    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            cin >> t;
            if (i <= j && t != -1) a.push_back(make_tuple(t,i,j));
        }
    }
    sort(a.begin(), a.end(), [](const tuple<int, int, int>& x, const tuple<int, int, int>& y) { return get<0>(x) < get<0>(y);} );
    for(auto e : a){
        if( !uf.same(get<1>(e), get<2>(e)) ){
            ans += get<0>(e);
            uf.unite(get<1>(e), get<2>(e));
        }
    }
    cout << ans << endl;
}