Go: package main

import (
	"bufio"
	"fmt"
	"log"
	"math"
	"os"
	"strconv"
	"strings"
)

type color int

const (
	white color = iota // 未訪問
	mst                // MSTとして確定
)

// 頂点
type node struct {
	matrix   []int // 隣接行列
	minToMst int   // MSTへの重み最小値
	parent   int   // 最小値の相手
	color    color
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n := eGetInt(scanner)

	nodes := make([]node, n)
	for i := 0; i < n; i++ {
		nodes[i].matrix = eAtoi((strings.Fields(eGetline(scanner))))
		nodes[i].parent = -1
		nodes[i].minToMst = math.MaxInt16
		nodes[i].color = white
	}

	// 初回はnode[0]がMSTに入るように,minToMstを設定
	nodes[0].minToMst = 0
	for { // 全部チェックするまで

		// どの頂点を新たにMSTに取り込むか
		min := math.MaxInt16
		u := -1
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].minToMst < min {
				u = i
				min = nodes[i].minToMst
			}
		}

		if u == -1 {
			break
		}
		// MSTに追加する頂点決定
		nodes[u].color = mst

		// MSTに属していない頂点それぞれについて,MSTとの最小の重みを更新
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].matrix[u] == -1 {
				// 接してない
				continue
			}
			if nodes[i].matrix[u] < nodes[i].minToMst {
				// node[u]との重みが最小
				nodes[i].minToMst = nodes[i].matrix[u]
				nodes[i].parent = u
			}
		}
	}

	sum := 0
	for _, v := range nodes {
		// node[0]はparentが入っていない
		if v.parent != -1 {
			sum += v.matrix[v.parent]
		}
	}
	fmt.Println(sum)
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

C++: #include<iostream>
#include<utility>
#include<algorithm>
using namespace std;
int matrix[100][100];
pair<int,int> edges[100];
int cost[100];
int src[100];
int dst[100];
int p[10010];
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 (p[a]=root(p[a]));
};
bool is_same_set(int a,int b)
{
    return root(a)==root(b);
};
void unite(int a,int b)
{
    p[root(a)]=root(b);
};

int main()
{
    int n,amount=0,sum=0;
    
    cin>>n;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cin>>matrix[i][j];
        }
    }
    
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<=i;j++)
        {
            if(matrix[i][j]!=-1)
            {
                cost[amount]=matrix[i][j];
                src[amount]=i;
                dst[amount]=j;
                amount++;
            }
        }
    }
    for(int i=0;i<amount;i++)
    {
        edges[i]=make_pair(cost[i],i);
    }

	init(n);
    
    sort(edges,edges+amount);
    
    for(int i=0;i<amount;i++)
    {
        if(is_same_set(src[edges[i].second()],dst[edges[i].second()]))
			continue;
		unite(src[edges[i].second()],dst[edges[i].second()]));
		sum+=edges[i].first();
    }
	cout<<sum<<endl;
}

C++: #include <iostream>
using namespace std;
#define INF 1000000

int main(){
  int n;
  int G[100][100],d[100];
  int minc,mi,i;
  bool flg[i];
  int sum=0;
  
  cin >> n;
  for (i=0;i<n;i++){
    for (int j=0;j<n;j++){
      cin >> G[i][j];
      if (G[i][j]==-1) G[i][j]=INF;
    }
    d[i]=INF;
    flg[i]=false;
  }

  d[0]=0;
  while (true){
    minc=INF;
    for (i=0;i<n;i++){
      if (!flg[i]&&d[i]<minc){
	minc=d[i];
	mi=i;
      }
    }
    if (minc==INF) break;
    flg[mi]=true;
    for (i=0;i<n;i++){
      if (G[mi][i]==INF)continue;
      if (!flg[i]&&d[i]>G[mi][i]){
	d[i]=G[mi][i];
	//cout << d[i];
      }
    }
  }
  
  for (i=0;i<n;i++){
    sum+=d[i];
  }
  cout << sum<<endl;
  
  return 0;
}

C++: #include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<iostream>
#include<stack>
#include<vector>
#define INFTY 10000
#define WHITE 0
#define GRAY 1
#define BLACK 2
using namespace std;

int color[120],d[120];
int M[120][120];
int n;

int start(int x){
  d[x]=0;
  while(true){
    int minimumd=INFTY,u;
    for(int i=0;i<n;i++){
      if(color[i]!=BLACK && minimumd>d[i]){
        minimumd=d[i];
        u=i;
      }
    }
    if(minimumd==INFTY) break;
    color[u]=BLACK;
    for(int i=0;i<n;i++){
      if(d[i]>M[u][i] && color[i]!=BLACK){
        d[i]=M[u][i];
        color[i]=GRAY;
      }
    }
  }
  int sum=0;
  for(int i=0;i<n;i++){
    sum+=d[i];
  }
  return sum;
}

int main(){
  int temp;
  cin>>n;
  for(int i=0;i<n;i++){
    d[i]=INFTY;
  }
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      cin>>temp;
      M[i][j]=(temp==-1)? INFTY : temp; 
    }
  }
  d[0]=0;
  int ans=start(0);
  cout<<ans<<endl;
}

C++: #include<iostream>
using namespace std;
#define INFTY (1 << 30)

enum Color {
	WHITE,
	GRAY,
	BLACK,
};

void Prim(int verValWeight[][100], int verNum) {
	int distance[100];
	Color color[100];
	int parent[100];
	for (int i = 0; i < verNum; i++) {
		color[i] = WHITE;
		distance[i] = INFTY;
		parent[i] = -1;
	}
	distance[0] = 0;

	while (true) {
		int min_cost = INFTY;
		int subScript;
		for (int i = 0; i < verNum; i++) {
			if (color[i] != BLACK && distance[i] < min_cost) {
				min_cost = distance[i];
				subScript = i;
			}
		}

		if (min_cost == INFTY)
			break; //end

		color[subScript] = BLACK;

		for (int i = 0; i < verNum; i++) {
			if (color[i] != BLACK && verValWeight[subScript][i] != INFTY) {
				if (verValWeight[subScript][i] < distance[i]) {
					distance[i] = verValWeight[subScript][i];
					parent[i] = subScript;
					color[i] = GRAY;
				}
			}
		}
	}

	int weight_sum = 0;
	for (int i = 0; i < verNum; i++)
		weight_sum += distance[i];
		//if (parent[i] != -1)
		//	weight_sum += verValWeight[i][parent[i]];
	cout << weight_sum << endl;

}

int main() {
	int verNum;
	int verValWeight[100][100];
	int parent[100];

	cin >> verNum;
	for (int i = 0; i < verNum; i++)
		for (int j = 0; j < verNum; j++) {
			cin >> verValWeight[i][j];
			if (verValWeight[i][j] == -1) verValWeight[i][j] = INFTY;
		}

	Prim(verValWeight, verNum);

	return 0;
}

C++: #include<cstdio>
#include<algorithm>
#include<queue>
#include<map>
using namespace std;
typedef pair< int, int > Pi;
const int INF = 1 << 30;
int info[100][100];
bool used[100];

int prim(const int& V){
  fill_n( used, V, false);
  priority_queue< Pi, vector< Pi >, greater< Pi > > que;
  que.push(Pi( 0, 0));
  int ret = 0;
  while(!que.empty()){
    Pi p = que.top();
    que.pop();
    if(used[p.second]++) continue;
    ret += p.first;
    for(int i = 0 ; i < V ; i++){
      if(~info[p.second][i]) que.push( Pi( info[p.second][i], i));
    }
  }
  return ret;
}

int main(){
  int N;
  scanf("%d", &N);
  for(int i = 0; i < N; i++){
    for(int j = 0 ; j < N ; j++){
      scanf("%d", &info[i][j]);
    }
  }
  printf("%d\n", prim(N));
}