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 <iostream>
#include<cstdio>
using namespace std;
const int INF = 20001;
static int G[100][100];

int prim(int n){
    
    const int BLACK = 2,GRAY = 1,WHITE =  0;
    int color[n],d[n];
    for(int i = 0;i < n;++i){
        d[i] = INF;
        color[i] = WHITE;
    }
    d[0] = 0;
    int min = INF,u;
    while(1){
        int min = INF;
        for(int i=0;i < n;++i){
            if(color[i] != BLACK && d[i] < min){
                min = d[i];
                u = i;
            }
        }
        if(min == INF) break;
        color[u] = BLACK;
        for(int i=0;i < n;++i){
            if(color[i] != BLACK && G[u][i] != INF){
                if(d[i] > G[u][i]){
                    d[i] = G[u][i];
                    color[i] = GRAY;
                }
            }
        }
        //for(int i = 0;i < n;++i) printf("%d ",d[i]);
    }
    int sum = 0;
    for(int i = 0;i < n;i++) sum += d[i];
    return sum;
}

int main(void){
    int n;
    scanf("%d",&n);
    for(int i = 0;i < n;++i){
        for(int j = 0;j < n;++j){
            scanf("%d",&G[i][j]);
            G[i][j] = (G[i][j] == -1) ? INF:G[i][j];
        }
    }

    printf("%d\n",prim(n));
    
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
using namespace std;
int P[1010];

void init(int N)
{
    for(int i = 1; i <= N; ++i)
    {
        P[i] = i;
    }
}
 
int root(int a)
{
    if(P[a] == a)
    {
        return a;
    }
    return (P[a] = root(P[a]));
}
 
bool is_same_set(int a, int b)
{
    return root(a) == root(b);
}
 
void unite(int a, int b)
{
    P[root(a)] = root(b);
}

int main()
{
	int n = 0;
	cin >> n; 
	int cost[5000];
	int src[5000];
	int dst[5000];
	int A[100 + 10][100 + 10];
	int M = 0;
	vector<pair<int,int>> edges;

	for(int r = 0; r < n; ++r)
	{
		for(int c = 0; c < n; ++c)
		{
			cin >> A[r][c];
		}
	}
	
	for (int r = 0; r < n; ++r)
	{
		for(int c = r + 1; c < n; ++c)
		{
			if(A[r][c] > -1)
			{
				cost[M] = A[r][c];
				src[M] = r;
				dst[M] = c;
				edges.push_back(make_pair(cost[M],M));
				M += 1;
			}
		}
	}
	sort(edges.begin(),edges.end());
	int sum = 0;
	init(n);
	for(int i = 0; i < M; ++i)
	{
		if(is_same_set(src[edges[i].second], dst[edges[i].second]) == 1) continue;
			unite(dst[edges[i].second],src[edges[i].second]);
			sum += edges[i].first;
	}
	cout << sum << endl;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define inf 1e9+7
typedef long long ll;

int n;
vector<vector<int> > cost;

void solve(int s){
    vector<bool> flg(n,false);
    flg[s]=true;
    vector<int> vc;
    vc.push_back(s);


    int sum=0;
    int mi,next;
    while(1){
        mi=inf;
        next=-1;
        for(int i=0;i<vc.size();i++){
            for(int j=0;j<n;j++){
                if(flg[j]||cost[vc[i]][j]<0)continue;
                if(mi>cost[vc[i]][j]){
                    mi=cost[vc[i]][j];
                    next=j;
                }
            }
        }
        if(next==-1)break;
        else{
            sum+=mi;
            flg[next]=true;
            vc.push_back(next);
        }
    }
    cout << sum << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    cin >> n;
    cost.resize(n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            int a;
            cin >> a;
            cost[i].push_back(a);

        }
    }

    solve(0);
    return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<algorithm>
#include<functional>
#define ll long long
#define inf  999999999
#define pa pair<int,int>

using namespace std;

int n,a[200][200]={0};
void prim(){
	int d[200]={0};
	priority_queue<pair<int,pa> >  PQ; 
	pair<int,pa> q;
	pa r;
	int wei=0;
	int u=0,z=0;
	d[0]=1;
	while(z!=n-1){
		for(int j=0;j<n;j++){
			if(a[u][j]<0) PQ.push(make_pair(a[u][j],make_pair(u,j)));
		}
	while(1){
		if(PQ.size()==0) {
		//	cout<<"dv"<<endl;
		break;
		}
		q=PQ.top();
		PQ.pop();
		r=q.second;
	//	cout<<"rsec"<<r.second<<endl;
		if(d[r.second]==0) break;
		
	}
	u=r.second;
//	cout<<"a" <<u<<endl;
	d[u]=1;
	wei=wei+q.first;
	z++;
//	cout<<q.first<<endl;
	}
	cout<<-wei<<endl;
}



int main(){
	// your code goes here
	int m;
	cin>>n;
	
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
		cin>>m;
		a[i][j]=-m;
		}
	}
	prim();

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define inf 1e9+7
typedef long long ll;

int n;
vector<vector<int> > cost;

void solve(int s){
    vector<bool> flg(n,false);
    flg[s]=true;
    vector<int> vc;
    vc.push_back(s);


    int sum=0;
    int mi,next;
    while(1){
        mi=inf;
        next=-1;
        for(int i=0;i<vc.size();i++){
            for(int j=0;j<n;j++){
                if(flg[j]||cost[vc[i]][j]<0)continue;
                if(mi>cost[vc[i]][j]){
                    mi=cost[vc[i]][j];
                    next=j;
                }
            }
        }
        if(next==-1)break;
        else{
            sum+=mi;
            flg[next]=true;
            vc.push_back(next);
        }
    }
    cout << sum << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    cin >> n;
    cost.resize(n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            int a;
            cin >> a;
            cost[i].push_back(a);

        }
    }

    solve(0);
    return 0;
}