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 <vector>
#include <algorithm>

using namespace std;
struct edge {
    edge() {};
    edge(int s, int e, int d) : start {s}, end {e}, d {d} {};
    bool operator<(edge y){
        return d < y.d || start < y.start || end < y.end;
    };
    bool operator>(edge y){
        return d > y.d || start > y.start || end > y.end;
    };
    bool operator==(edge y){
        return d == y.d || start == y.start || end || y.end;
    };
    int start;
    int end;
    int d;
};

void dfs(vector<vector<int>> graph, bool* used, int id, int n){
    used[id] = true;
    for(int i = 0; i < n; ++i){
        if(graph[id][i] != -1 || used[i]){
            continue;
        }
        dfs(graph, used, i, n);
    }
}

bool is_connected(vector<vector<int>>& graph){
    int n = graph.size();
    bool used[n];
    for(int i = 0; i < n; ++i){
        used[i] = false;
    }
    dfs(graph, used, 0, n);
    for(int i = 0; i < n; ++i){
        if(!used[i]){
            return false;
        }
    }
    return true;
}

void delete_edges(vector<vector<int>>& graph){
    int edges_num = 0;
    vector<edge> vec {};
    int n = graph.size();
    for(int i = 0; i < n; ++i){
        for(int j = i+1; j < n; ++j){
            if(graph[i][j] != -1){
                ++edges_num;
                vec.push_back(edge(i, j, graph[i][j]));
            }
        }
    }
    sort(vec.begin(), vec.end(), [](edge x, edge y){
            return y.d < x.d;
         });

    for(auto it = vec.begin(); it != vec.end(); ++it){
        edge e = *it;
        graph[e.start][e.end] = -1;
        graph[e.end][e.start] = -1;
        if(is_connected(graph)){
            --edges_num;
            if(edges_num == n-1){
                return;
            }
        } else {
            graph[e.start][e.end] = e.d;
            graph[e.end][e.start] = e.d;
        }
    }
}

vector<vector<int>> gen_spanning_tree(vector<vector<int>>& graph){
    vector<vector<int>> tree {graph};
    delete_edges(tree);
    return tree;

}

int calc_weight(vector<vector<int>> graph){
    int sum = 0;
    int n = graph.size();
    for(int i = 0; i < n; ++i){
        for(int j = i+1; j < n; ++j){
            if(graph[i][j] == -1){
                continue;
            }
            sum += graph[i][j];
        }
    }
    return sum;
}

int main(){
    int n;
    cin >> n;
    vector<vector<int>> graph {n, vector<int>(n, 0)};
    for(int i = 0; i < n; ++i){
        for(int j = 0; j < n; ++j){
            cin >> graph[i][j];
        }
    }
    auto tree = gen_spanning_tree(graph);
    cout << calc_weight(tree) << endl;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define MAX 100
#define INF 1<<25
int n,cost[MAX][MAX];
int mincost[MAX];
bool used[MAX];
int prim(){
  for(int i=0;i<n;i++)mincost[i]=INF,used[i]=false;
    mincost[0]=0;
  int res=0;
  while(1){
    int v=-1;
    for(int u=0;u<n;u++)
      if(!used[u]&&(v==-1||mincost[u]<mincost[v]))v=u;
    if(v==-1)break;
    used[v]=1;
    res+=mincost[v];
    for(int u=0;u<n;u++)mincost[u]=min(mincost[u],cost[v][u]);
  }
return res;
}
int main(){
  cin>>n;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      int e;
      cin>>e;
      cost[i][j]=(e==-1)?INF:e;
    }
  }
  cout<<prim()<<endl;
}

C++: #include <iostream>
#include <vector>
#include <queue>
#include <cmath>
#include <algorithm>
#include <utility>

using namespace std;

// int search_xyz(int e);
int tree[100];

int root(int a);
bool is_same_set(int p, int q);
void joint(int x, int y);

int main()
{
    int n, tempa, k = 0;
    cin >> n;
    int e = n * (n - 1) / 2;
    pair<int, pair<int, int>

         >
        a[e];
    for (int i = 0; i < n; i++)
    {
        tree[i] = i;
        for (int j = 0; j < n; j++)
        {
            cin >> tempa;
            if (i < j)
            {
                a[k] = make_pair(tempa, make_pair(i, j));
                k++;
            }
        }
    }
    sort(a, a + e);
    int result = 0;
    for (int i = 0; i < e; i++)
    {
        if (a[i].first == -1)
            continue;

        if (is_same_set(a[i].second.first, a[i].second.second))
        {
            continue;
        }
        else
        {
            joint(a[i].second.first, a[i].second.second);
            result += a[i].first;
        }
    }
    cout << result << endl;
    return 0;
}

int root(int a)
{
    if (tree[a] == a)
    {
        return a;
    }
    else
    {
        tree[a] = root(tree[a]);
        return tree[a];
    }
}

bool is_same_set(int p, int q)
{
    return root(p) == root(q);
}

void joint(int x, int y)
{
    tree[root(x)] = root(y);
}

C++: #include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
#include <string>
#include <queue>
using namespace std;
const int MAXN = 10005;
const int INF = 1 << 30;
const int NIL = -1;
struct Node {
	int v, w, next;	//u->v
	friend bool operator<(const Node& a, const Node& b)
	{
		return a.w > b.w;
	}
	Node() {}
	Node(int vv, int ww) : v(vv), w(ww) {}
};
int cnt;
int head[MAXN];
Node edge[MAXN];




int prim(int n)
{
	
	bool vis[MAXN]{ false };
	priority_queue<Node> q;
	vis[1] = true;

	for (int i = head[1]; i != NIL; i = edge[i].next)
		q.push(edge[i]);
	int count = 0;
	int ans = 0;
	Node t;
	while (count < n - 1)
	{
		t = q.top();
		q.pop();
		if (vis[t.v])
			continue;
		vis[t.v] = true;
		ans += t.w;
		++count;
		for (int i = head[t.v]; i != NIL; i = edge[i].next)
			if (!vis[edge[i].v])
				q.push(edge[i]);

	}
	
	return ans;
}


void add(int u, int v, int w)
{
	edge[cnt].v = v;
	edge[cnt].w = w;
	edge[cnt].next = head[u];
	head[u] = cnt++;
}



int main(void)
{
	int n, m, u, v, w;
	scanf("%d", &n);
	int N = n * n;
	for (int i = 0; i <= N; ++i)
		head[i] = NIL;
	cnt = 0;
	for (int i = 1; i <= n; ++i)
	{
		for (int j = 1; j <= n; ++j)
		{
			scanf("%d", &w);
			if (w != NIL)
				add(i, j, w);
		}
	}
	cout << prim(n) << endl;
	return 0;
}