Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] >= 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A >= edges[j].A })

	sum := 0
	num := 0
	for len(edges) > 0 && num < n-1 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
		num += 1
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

C++: #include <iostream>
#include <set>
#include <queue>

using namespace std;
using P = pair<int, int>;

const int MAX = 100;
const int NIL = -1;

int G[MAX][MAX];

int main() {

    int n;
    cin >> n;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> G[i][j];
        }
    }

    set<int> T;
    int sum = 0;

    T.insert(0);

    while (T.size() < n) {
        priority_queue<P, vector<P>, greater<>> pq;
        for (int u : T) {
            for (int i = 0; i < n; i++) {
                if (G[u][i] != NIL && T.find(i) == T.end()) {
                    pq.push(make_pair(G[u][i], i));
                }
            }
        }
        T.insert(pq.top().second);
        sum += pq.top().first;
    }

    cout << sum << endl;
}

C++: #include<ostream>
#include<cstdio>
using namespace std;
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;
static const int INFTY=(1<<21);
int n,H[100][100];
int p()
{
    int u,minv,d[100],p[100],c[100];
    for(int i=0;i<n;i++)
    {
        d[i]=INFTY;
        p[i]=-1;
    }
    d[0]=0;
    while(1)
    {
        minv=INFTY;
        u=-1;
        for(int i=0;i<n;i++)
        {
            if(minv>d[i]&&c[i]!=BLACK)
            {
                u=i;
                minv=d[i];
            }
        }
        if(u==-1) break;
        c[u]=BLACK;
        for(int v=0;v<n;v++)
        {
            if(c[v]!=BLACK&&H[u][v]!=INFTY)
            {
                if(d[v]>H[u][v])
                {
                    d[v]=H[u][v];
                    p[v]=u;
                    c[v]=GRAY;
                }
            }
        }
    }
    int sum=0;
    for(int i=0;i<n;i++)
    {
        if(p[i]!=-1) sum+=H[i][p[i]];
    }
    return sum;
}
int main()
{
    int a;
    scanf("%d",&n);
    for(int i=0;i<n;i++)
        for(int j=0;j<n;j++)
    {
        scanf("%d",&a);
        H[i][j]=(a==-1)?INFTY:a;
    }
    printf("%d\n",p());
    return 0;
}

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

#define int long long

struct edge{
  int u, v, cost;
  bool operator < (edge const& other){
	  return cost < other.cost;  
	}	
};

const int N = 100 + 11;
int p[N], sz[N];
vector<edge> edge_list;
vector<edge> ret;
int weight;

int get(int x){
  if (p[x] == x) return x;
  return p[x] = get(p[x]);	
}

void unite(int x, int y){
  x = get(x), y = get(y);
  if (sz[x] < sz[y]) swap(x, y);
  sz[x] += sz[y];
  p[y] = x;
}

void KruskalMST( vector<edge> &edge_list){
	sort(edge_list.begin(), edge_list.end());
	for(auto it : edge_list){
	  if (get(it.u)  != get(it.v)){
	    unite(it.u, it.v);
	    weight += it.cost;
	    ret.push_back(it);	  
     }	
  }	
}

int32_t main(){
  	int n;
  	cin >> n;
  	vector<edge> g;
  	for(int i = 0; i < n; i++){
	  p[i] = i;
	  sz[i] = 0;	
	}
  	for (int i = 0; i < n; i++){
	  for (int j = 0; j < n; j++){
		  int x;
		  cin >> x;
		  if ( x != -1) g.push_back({i, j, x});  
	  }	
	}
  KruskalMST(g);
  cout << weight << endl;
}

C++: #include <iostream>
using namespace std;
#define MAX 100
#define INFINITY (1<<30)
enum{
	white=0,
	gray=1,
	black=2,
};

int n,m[MAX][MAX];

int prim(){
	int u,minv;
	int d[MAX],p[MAX],color[MAX];
	for(int i=0;i<n;i++){
		d[i]=INFINITY;
		p[i]=-1;
		color[i]=white;
	}
	d[0]=0;
	while(1){
		minv=INFINITY;
		u=-1;
		for(int i=0;i<n;i++){
			if(minv>d[i]&&color[i]!=black){
				u=i;
				minv=d[i];
			}
		}
		if(u==-1)	break;
		color[u]=black;
		for(int v=0;v<n;v++){
			if(color[v]!=black&&m[u][v]!=INFINITY){
				if(d[v]>m[u][v]){
					d[v]=m[u][v];
					p[v]=u;
					color[v]=gray;
				}
			}
		}
	}
	int sum=0;
	for(int i=0;i<n;i++){
		if(p[i]!=-1)	sum+=m[i][p[i]];
	}
	return sum;
}

int main(){
	cin>>n;
	int e;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin>>e;
			if(e==-1)	m[i][j]=INFINITY;
			else	m[i][j]=e;
		}
	}
	cout<<prim()<<endl;
	return 0;
}