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>
#include<vector>
#include<queue>
#include<algorithm>
//#include<operator>

using namespace std;


class UFT{
public:
  int P[10010];//その頂点の親を格納する

  //初めは全ての頂点はバラバラで違うグループに属する
  void init(int N){
    for(int i=0;i<N;i++) P[i]=i;
  }

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

  bool is_same_set(int a,int b){
    return root(a)==root(b);
  }

  void unite(int a,int b){
    //aのルートだったもののルートをbのルートにする
    P[root(a)]=root(b);
  }
};

bool is_same_set_all(UFT a,int n){
  for(int i=0;i<n-1;i++){
    if(!(a.is_same_set(i,i+1))){return false;}
  }
  return true;
}

class edge{
public:
  int from_Node;
  int to_Node;
  int cost;
};

//本来は<さえオーバーロードすれば大丈夫が四つのオペレータをオーバロードしなければならなかった(何故？？)
bool operator< (const edge& e1,const edge& e2){
  return e1.cost < e2.cost;
}


bool operator> (const edge& e1,const edge& e2){
  return e1.cost > e2.cost;
}


bool operator<= (const edge& e1,const edge& e2){
  return e1.cost <= e2.cost;
}

bool operator>= (const edge& e1,const edge& e2){
  return e1.cost >= e2.cost;
}


int main(){
  #if 0
  このようにデバッグができる(比較演算子のオーバーロード)
  edge a={0,1,2},b={1,2,3};
  if(a<b){cout << "a<b" << endl;}
  if(b<a){cout << "b<a" << endl;}
  if(a>b){cout << "a>b" << endl;}
  if(a<=b){cout << "a<=b" << endl;}
  #endif


  int n;cin >> n;
  priority_queue<
  edge,//要素の型
  vector<edge>,//内部コンテナはvectorで(デフォ)
  greater<edge>//昇順
  > ve;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      edge e;int c;
      cin >> c;
      if(c!=-1 and i<j){
        e.from_Node=i;e.to_Node=j;e.cost=c;
        ve.push(e);
      }
    }
  }
  UFT G;G.init(n);
  int co=0;
  while(!(is_same_set_all(G,n))){
    if(!(G.is_same_set(ve.top().from_Node,ve.top().to_Node))){
      G.unite(ve.top().from_Node,ve.top().to_Node);
      co+=ve.top().cost;
      ve.pop();
    }else{
      ve.pop();
    }
  }
  cout << co << endl;

}

C++: #include <bits/stdc++.h>
#define MAX 20000
using namespace std;

int main(void){
  ios::sync_with_stdio(false);
  cin.tie(0);

  int n; cin >> n;
  vector< vector<int> > v(n, vector<int>(n));
  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> v[i][j];
      if(v[i][j] == -1) v[i][j] = MAX;
    }
  }

  vector<int> cost(n, MAX), used(n, false);
  cost[0] = 0;
  int ans = 0;
  int t;

  while(true){
    t = -1;
    for(int i = 0; i < n; i++){
      if(!used[i] && (t == -1 || cost[t] > cost[i])) t = i;
    }
    if(t == -1) break;
    used[t] = true;
    ans += cost[t];

    for(int i = 0; i < n; i++){
      cost[i] = min(cost[i], v[t][i]);
    }
  }

  cout << ans << endl;

  return 0;
}