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<iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1<<21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int 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]=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){
        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]!=INFTY){
        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;

  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      int e;
      cin >> e;
      M[i][j]=(e==-1) ? INFTY:e;
    }
  }
  cout << prim() << endl;
  return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <queue>
#include <list>
#include <stack>
#include <string>
#include <tuple>
#include <functional>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <map>
#include <random>
#include <cstdlib>
#define INT_MAX 2147483647
#define INT_MIN -2147483646
#define Loop(i, n) for(int i = 0; i < (int)n; i++)
#define Loop1(i, n) for(int i = 1; i <= (int)n; i++)
#define Loopr(i, n) for(int i = (int)n - 1; i >= 0; i--)
#define Loopr1(i, n) for(int i = (int)n; i >= 1; i--)
using namespace std;
typedef long long int ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;

static const int N = 105;

struct vertex {
	int id;
	int p;
	int d;
	bool operator<(const vertex & another) const {
		return (d != another.d ? d>another.d : id>another.id);
	}
};

int main() {
	vvi mx(N, vi(N, -1));
	int n;
	cin >> n;
	Loop(i, n) {
		Loop(j, n) {
			int a;
			cin >> a;
			mx[i][j] = a;
		}
	}
	
	vector<bool> color(N, 0);
	priority_queue<vertex> q;
	q.push({ 0,-1,0});
	int ret = 0;
	while(q.size() > 0) {
		vertex v = q.top();
		q.pop();
		if (color[v.id] == 1) continue;
		color[v.id] = 1;
		ret += v.d;
		Loop(j, n) {
			if (mx[v.id][j] != -1 && color[j] != 1){
				q.push({ j, v.id,mx[v.id][j] });
			}
		}
	}
	cout << ret << endl;
	return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <numeric>
#include <vector>

using namespace std;

template <class T>
struct Edge {
    int from, to;
    T cost;
    Edge(int from, int to, T cost) : from(from), to(to), cost(cost){};

    bool operator<(const Edge<T>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<T>& e) const { return this->cost > e.cost; }
};

template <class T = int>
class Graph {
public:
    explicit Graph(int N = 0) : size(N) { path.resize(size); }
    void span(int u, int v, T cost = 1) { path[u].push_back(Edge<T>(u, v, cost)); }
    vector<Edge<T>> operator[](int v) const { return path[v]; }

    int size;
    vector<vector<Edge<T>>> path;
};

class UnionFind {
public:
    vector<int> par, num;

    explicit UnionFind(int N) {
        par.resize(N);
        iota(par.begin(), par.end(), 0);
        num.assign(N, 1);
    }

    int find(int v) {
        return (par[v] == v) ? v : (par[v] = find(par[v]));
    }

    void unite(int u, int v) {
        u = find(u), v = find(v);
        if (u == v) return;

        if (num[u] < num[v]) swap(u, v);
        num[u] += num[v];
        par[v] = u;
    }

    bool same(int u, int v) { return find(u) == find(v); }
    bool ispar(int v) { return v == find(v); }
    int size(int v) { return num[find(v)]; }
};

int main() {
    int N;
    cin >> N;
    vector<Edge<int>> edges;
    for (int u = 0; u < N; ++u) {
        for (int v = 0; v < N; ++v) {
            int c;
            cin >> c;
            if (u < v && c >= 0) edges.push_back(Edge<int>(u, v, c));
        }
    }
    sort(edges.begin(), edges.end());

    int ans = 0;
    UnionFind uf(N);
    for (const auto& e : edges) {
        if (uf.same(e.from, e.to)) continue;
        ans += e.cost;
        uf.unite(e.from, e.to);
    }

    cout << ans << endl;
    return 0;
}