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<queue>
using namespace std;

struct Data{

  int weight;
  int s,g;

  bool operator < (const Data& p)const {
    if(weight != p.weight)return weight > p.weight;
    if(s != p.s)return s > p.s;
    return g > p.g;
  }
  
};

int par[100],rank[100];
priority_queue<Data> data;

int find(int x){
  
  if( x == par[x]){
    return x;
  }else{
    par[x]=find(par[x]);
  }
  return par[x];
}
bool same(int x,int y){
  if(find(x) == find(y)){
    return true;
  }else{
    return false;
  }
}
void unite(int x,int y){
  
  int x_oya,y_oya;
  
  x_oya=find(x);
  y_oya=find(y);
  
  if(rank[x_oya] > rank[y_oya]){
    par[x_oya]=par[y_oya];
  }else if(rank[x_oya] < rank[y_oya]){
    par[y_oya]=par[x_oya];
  }else{
    par[y_oya]=par[x_oya];
    rank[x_oya]++;
  }
  
}
int kruskal(void){
  
  Data a;
  int cost=0;
  
  while(!data.empty()){
    a=data.top();
    data.pop();
    if(!same(a.s,a.g)){
      cost+=a.weight;
      unite(a.s,a.g);
    }
  }
  return cost;
  
}
int main(){
  
  int n,weight;
  
  for(int i=0 ; i < 100 ; i++){
    par[i]=i;
    rank[i]=0;
  }
  
  cin >>n;

  for(int i=0 ; i < n ; i++){
    for(int j=0 ; j < n ; j++){
      cin >>weight;
      if(weight == -1)continue;
      data.push((Data){weight,i,j});
    }
  }
  
  cout <<kruskal()<<endl;

  return 0;
}

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

const int N=105;
int g[N][N];
int dist[N];
bool vis[N];
int n, ans=0;

void prim(){
    dist[0]=0;
    for(int i=0; i<n; ++i){
        int node=-1;
        for(int j=0; j<n; ++j){
            if(!vis[j] && (node==-1 || dist[j]<dist[node])) node=j;
        }
        if(node==-1) break;
        vis[node]=true;
        ans+=dist[node];
        for(int j=0; j<n; ++j) 
            if(g[node][j]!=-1) dist[j]=min(dist[j], g[node][j]);
    }
}

int main(){
    memset(dist, 0x3f, sizeof dist);
    memset(vis, 0x00, sizeof vis);
    cin>>n;
    for(int i=0; i<n; ++i)
        for(int j=0; j<n; ++j)
            cin>>g[i][j];
            
    prim();
    cout<<ans<<endl;
    return 0;
}

C++: #include <stdio.h>
#include <iostream>
#include <vector>
using namespace std;

#define N_MAX 100
#define WHITE 1
#define GREY 2
#define BLACK 3
#define INF 1000000000
#define NIL -1

int G[N_MAX][N_MAX];
int V[N_MAX];
int V_value[N_MAX];

void init(void){
    for(int i = 0; i < N_MAX; i++){
        V[i] = WHITE;
        V_value[i] = INF;
    }
}

int main(void){
    init();
    int n;
    scanf("%d\n", &n);

    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            scanf("%d", &G[i][j]);
        }
    }

    V[0] = BLACK;
    V_value[0] = 0;
    int new_node = 0;
    int sum = 0;
    while(1){
        for(int i = 0; i < n; i++){
            if(G[new_node][i] != -1 && V[i] == WHITE){
                V_value[i] = min(V_value[i], G[new_node][i]);
            }
        }

        int min_value = INF;
        int min_index = NIL;
        for(int i = 0; i < n; i++){
            if(V[i] == WHITE){
                if(V_value[i] < min_value){
                    min_index = i;
                    min_value = V_value[i];
                }
            }
        }
        if(min_index == NIL){
            break;
        }else{
            V[min_index] = BLACK;
            new_node = min_index;
            sum += min_value;
        }
    }

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

C++: #include <algorithm>
#include <cstdint>

using namespace std;

enum status_t {
  WHITE,
  GRAY,
  BLACK,
};

#define GRAPH_SIZE 101

static uint32_t graph[GRAPH_SIZE][GRAPH_SIZE];
static status_t state[GRAPH_SIZE];
static uint32_t shortest_path[GRAPH_SIZE];

size_t minimum_spanning_tree(size_t num)
{
  size_t minimum_cost = 0;

  for (uint32_t i = 0; i < num; i++) {
    shortest_path[i] = UINT32_MAX;
    state[i] = WHITE;
  }

  shortest_path[0] = 0;
  state[0] = GRAY;

  while (true) {
    uint32_t minimum = UINT32_MAX;
    uint32_t to = 0;
    for (uint32_t j = 0; j < num; j++) {
      if ((shortest_path[j] < minimum) && state[j] != BLACK) {
        minimum = shortest_path[j];
        to = j;
      }
    }

    if (minimum == UINT32_MAX) break;

    state[to] = BLACK;
    minimum_cost += minimum;

    for (uint32_t j = 0; j < num; j++) {
      if (state[j] != BLACK) {
        shortest_path[j] = min(shortest_path[j], graph[to][j]);
      }
    }
  }

  return minimum_cost;
}

#include <iostream>

int32_t main()
{
  uint32_t num;
  cin >> num;

  for (uint32_t i = 0; i < num; i++) {
    for (uint32_t j = 0; j < num; j++) {
      int32_t val;
      cin >> val;
      if (val == -1) {
        graph[i][j] = UINT32_MAX;
      } else {
        graph[i][j] = val;
      }
    }
  }

  cout << minimum_spanning_tree(num) << endl;

  return 0;
}

C++: #include <iostream>
#include <queue>
#include <vector>
using namespace std;

const int MAX_V = 100010;
struct edge{ int cost, to; };


int V;
vector<edge> G[MAX_V];
bool used[MAX_V];

auto compare = [](edge a, edge b){
    return a.cost > b.cost;
};

int res = 0;
int prim_pq(int s){
    for(int i = 0; i < V; i++) used[i] = false;
    used[s] = true;
    
    priority_queue<edge,vector<edge>,decltype(compare)> pq{compare};
    for(int i = 0; i < G[s].size(); i++) pq.push(G[s][i]);
    
    while(!pq.empty()){
        edge e = pq.top(); pq.pop();
        if(used[e.to]) continue;
        used[e.to] = true;
        res += e.cost;
        for(int i = 0; i < G[e.to].size(); i++) pq.push(G[e.to][i]);
    }
    return res;
}

int main(){
    cin >> V;
    for(int i = 0; i < V; i++){
        for(int j = 0; j < V; j++){
            int x; cin >> x;
            if(x == -1) continue;
            edge e;
            e.to = j; e.cost = x;
            G[i].push_back(e);
        }
    }
    cout << prim_pq(0) << endl;
    return 0;
}

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

vector<int> P;
int n;

void init() {
  for (int i = 0; i < n; i++)
    P[i] = i;
}
int root(int c) {
  if (P[c] == c)
    return c;
  return (P[c] = root(P[c]));
}
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() {
  cin >> n;
  P = vector<int>(n);
  init();
  vector<tuple<int, int, int>> edges; //<weight, start, end>
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      int a;
      cin >> a;
      if (i > j && a != -1)
        edges.push_back(make_tuple(a, i, j));
    }
  }
  sort(edges.begin(), edges.end());

  int ans = 0;
  for (tuple<int, int, int> edge : edges) {
    int w = get<0>(edge), s = get<1>(edge), e = get<2>(edge);
    if (!is_same_set(s, e)) {
      unite(s, e);
      ans += w;
    }
  }
  cout << ans << endl;
}