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;

struct Node{
  int color, parent;
};

int n, M[MAX][MAX];
Node node[MAX];

void Printnodes(){
  string col[3] = {"WHITE", "GRAY ", "BLACK"};
  for(int i = 0; i < n; i++){
    cout << "nodeID : " << i ;
    cout << " color : " << col[node[i].color];
    cout << " parent : " << node[i].parent << endl;
  }
  cout << endl;
}

int main(){
  cin >> n;

  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> M[i][j];
    }
    node[i].color = WHITE;
    node[i].parent = -1;
  }

  node[0].color = BLACK;
  int totaldist = 0;

  while(true){
 //   Printnodes();

    int count = 0, min_d = INFTY, min_id, dist;
    for(int p = 0; p < n; p++){
      if(node[p].color == BLACK){
        for(int i = 0; i < n; i++){
          if(M[p][i] > 0 && node[i].color != BLACK){
            count++;
            node[i].color = GRAY;
            dist = M[p][i];
            if(dist < min_d){
              min_d = dist;
              min_id = i;
              node[i].parent = p;
            }
          }
        }
      }
    }

    if(count == 0)
      break;
    node[min_id].color = BLACK;
    totaldist += min_d;
  }

  cout << totaldist << endl;
  return 0;
}

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

using namespace std;
using MatrixGraph = vector<vector<int>>;

const int no_edege = -1;
const int started_label = 1;
const int no_label = -1;
const int no_cost = -1;
const int max_weight = 2'000;

int total_weight(MatrixGraph matrix_graph, int started_label) {
  vector<int> min_weights(matrix_graph.size(), max_weight + 1);
  vector<int> visited(matrix_graph.size(), false);
  min_weights[started_label - 1] = 0;
  int weight_sum = 0;

  while(true) {
    int min_weight = max_weight + 1;
    int min_label = no_label;
    for(int i = 0; i < matrix_graph.size(); i++) {
      if(visited[i]) {
        continue;
      }
      if(min_weights[i] < min_weight) {
        min_weight = min_weights[i];
        min_label = i + 1;
      }
    }
    if(min_label == no_label) {
      break;
    }

    visited[min_label - 1] = true;
    weight_sum += min_weight;

    for(int i = 0; i < matrix_graph.size(); i++) {
      if(matrix_graph[min_label - 1][i] < min_weights[i]) {
        min_weights[i] = matrix_graph[min_label - 1][i];
      }
    }
  }

  return weight_sum;
}

int main() {
  int vertex_num;
  cin >> vertex_num;
  MatrixGraph matrix_graph(vertex_num, vector<int>(vertex_num, no_edege));

  // Init
  for(int i = 0; i < vertex_num; i++) {
    for(int j = 0 ;j < vertex_num; j++) {
      int weight;
      cin >> weight;
      if(weight == no_edege) {
        matrix_graph[i][j] = max_weight + 1;
        continue;
      }
      matrix_graph[i][j] = weight;
    }
  }

  cout << total_weight(matrix_graph, started_label) << endl;
}

C++: #include <stdio.h>

#define inf 100000
#define WHITE 1
#define BLACK 0
#define MAX 100

int d[MAX],pi[MAX],color[MAX],A[MAX][MAX];
int n,i,j,v,u;
int min,count=0;

int main(){

  int i,j;

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

  for(i=0;i<n;i++){
    d[i]=inf;
    color[i]=WHITE;
  }
  d[0]=0;

  while(1){
    min=inf;
    for(i=0;i<n;i++){
      if(color[i]==WHITE && d[i]<min){
	min=d[i];
	u=i;
      }
    }

    if(min==inf)break;
    color[u]=BLACK;
    count+=min;

    for(v=0;v<n;v++){
      if(A[u][v]==-1)continue;
      if(d[v]>A[u][v])d[v]=A[u][v];
    }
  }

  printf("%d\n",count);

  return 0;
  
}

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

using namespace std; 

int main(void) {
	int nov;
	cin >> nov;
	vector< vector<int> > w(nov,vector<int>(nov));
	for (int i = 0; i < nov; ++i) {
		for (int j = 0; j < nov; ++j) {
			cin >> w[i][j];
		}
	}

	int wmin,v,res = 0;
	vector<int> term(nov,-1); 
	vector<int> check(nov,-1); 
	term[0] = 0;
	check[0] = 1;
	for (int i = 1; i < nov; ++i) {
		wmin = (1 << 28);
		for (int j = 0; j < i; ++j) {
			for (int k = 0; k < nov; ++k) {
				if (check[k] < 0 && w[term[j]][k] >= 0) {
					if (w[term[j]][k] < wmin) {
						wmin = w[term[j]][k];
						v = k;
					}
				}
			}
		}
		res += wmin;
		term[i] = v;
		check[v] = 1;
	}
	cout << res << endl;

	return 0;
}