Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

const INF = 1 << 60

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < N; i++ {
		G[i] = make([]int, N)
		for j := 0; j < N; j++ {
			G[i][j] = sc.nextInt()
		}
	}
	d := make([]int, N)
	for i := 0; i < N; i++ {
		d[i] = INF
	}
	seen := make([]bool, N)
	d[0] = 0
	ans := 0
	for {
		cur := 0
		minCost := INF
		for i := 0; i < N; i++ {
			if !seen[i] && d[i] < minCost {
				minCost = d[i]
				cur = i
			}
		}
		if minCost == INF {
			break
		}
		seen[cur] = true
		ans += d[cur]
		for i := 0; i < N; i++ {
			cost := G[cur][i]
			if cost != -1 && cost < d[i] {
				d[i] = cost
			}
		}
	}

	fmt.Fprintln(wtr, ans)
	wtr.Flush()
}

C++: #include <bits/stdc++.h>

using namespace std;

int n;
const int N = 110;
int A[N][N];
typedef pair<int, int> P;
vector<P> G[N];

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

vector<Edge> edges;
vector<int> parent(N), height(N);

int min_cost = 0;

void prim() {
    priority_queue<P, vector<P>, greater<P>> heap;
    heap.push({0, 1});
    vector<bool> vis(n + 1, false);
    vector<int> dis(n + 1, INT_MAX);

    while (!heap.empty()) {
        int u = heap.top().second, cost = heap.top().first;
        heap.pop();
        if (vis[u]) continue;
        vis[u] = true;
        min_cost += cost;
        for (int i = 0; i < G[u].size(); i++) {
            int v = G[u][i].second, len = G[u][i].first;
            if (!vis[v] && len < dis[v]) {
                dis[v] = len;
                heap.push({len, v});
            }
        }
    }    
}

void init() {
  for (int i = 1; i <= n; i++) {
    parent[i] = i;
    height[i] = 1;
  }
}

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

void merge(int x, int y) {
    x = find(x), y = find(y);
    if (x == y) return;
    if (height[x] < height[y]) {
        parent[x] = y;
    } else {
        parent[y] = x;
        if (height[x] == height[y]) height[x]++;
    }
}

void kruskal() {
    sort(edges.begin(), edges.end());
    init();
    for (auto &edge : edges) {
        int u = edge.u, v = edge.v, cost = edge.cost;
        
        if (find(u) != find(v)) {
            merge(u, v);
            min_cost += cost;
        }
    }
}

int main() {
    cin >> n;
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            cin >> A[i][j];
        }
    }

    for (int i = 1; i <= n; i++) {
        for (int j = i + 1; j <= n; j++) {
            if (A[i][j] != -1)
            edges.push_back({i, j, A[i][j]});
        }
    }

    kruskal();
    // prim();
    cout << min_cost << endl;

    return 0;
}

C++: #include<iostream>
#include<cstring>
using namespace std;
#define maxn 110
#define INFTY (1<<30)
#define WHITE 0
#define GRAY 1
#define BLACK 2
int n,m[maxn][maxn];

int prim() //返回最小生成树各边权值总和
{
    int u,minv;
    int d[maxn],p[maxn],color[maxn];

    for(int i=0;i<n;i++) //初始化
    {
        d[i]=INFTY;
        p[i]=-1;
        color[i]=WHITE;
    }
    d[0]=0;

    while(1)
    {
        minv=INFTY;
        u=-1;
        for(int i=0;i<n;i++)
        {
            if(minv>d[i]&&color[i]!=BLACK) //寻找最小权值的边
            {
                u=i;
                minv=d[i];
            }
        }
        if(u==-1) break;
        color[u]=BLACK; //标记为黑
        for(int v=0;v<n;v++)
        {
            if(color[v]!=BLACK&&m[u][v]!=INFTY) //如果u和v之间存在边
            {
                if(m[u][v]<d[v]) //注意这里是d[v]不是d[u]
                {
                    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;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cin>>m[i][j];
            if(m[i][j]==-1) m[i][j]=INFTY;
        }
    }
    cout<<prim()<<endl;
    return 0;
}

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

constexpr int INF = 1e9;

struct edge {
	int from, to, cost;
	bool operator>(const edge& other)const {
		return cost > other.cost;
	}
};

using edges = vector<edge>;
using graph = vector<edges>;

void add_edge(graph& g, int from, int to, int cost) {
	g[from].push_back(edge{ from,to,cost });
	g[to].push_back(edge{ to,from,cost });
}


edges prim(const graph& g) {
	const int N = g.size();
	vector<bool>used(N);
	used[0] = true;
	priority_queue<edge, vector<edge>, greater<edge>>p_que;
	for (auto e : g[0]) {
		p_que.push(e);
	}
	edges mst;
	while (!p_que.empty()) {
		auto e = p_que.top();
		p_que.pop();
		if (used[e.to]) {
			continue;
		}
		mst.push_back(e);
		used[e.to] = true;
		for (auto new_e : g[e.to]) {
			p_que.push(new_e);
		}

	}
	return mst;
}

int main() {
	int V, E;
	cin >> V >> E;
	graph g(V);
	for (int i = 0; i < E; i++) {
		int from, to, cost;
		cin >> from >> to >> cost;
		add_edge(g, from, to, cost);
	}
	const auto mst = prim(g);
	int ans = 0;
	for (auto& e : mst) {
		ans += e.cost;
	}
	cout << ans << endl;
	return 0;
}