Go: package main

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

//util
var sc = bufio.NewScanner(os.Stdin)

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

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX   = 100
	INFTY = (1 << 21)
	WHITE = 0
	GRAY  = 1
	BLACK = 2
)

//V: グラフの頂点全体の集合
//T: MSTに属する頂点の集合
var (
	n     int
	M     [MAX][MAX]int //重みを記録する隣接行列
	color [MAX]int
	p     [MAX]int //MSTにおける頂点の親を記録
	d     [MAX]int //Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを記録
)

func prim() int {
	var u, minv int
	//初期化
	for i := 0; i < n; i++ {
		d[i] = INFTY
		p[i] = -1
		color[i] = WHITE
	}

	d[0] = 0

	for {
		//頂点uを決めていく
		//つまり、Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを決める
		minv = INFTY
		u = -1
		for i := 0; i < n; i++ {
			//未訪問かつ、辺の重みが最小となるuを選ぶ
			if minv > d[i] && color[i] != BLACK {
				u = i
				minv = d[i]
			}
		}

		if u == -1 {
			break
		}

		color[u] = BLACK
		for v := 0; v < n; v++ {
			//未訪問かつ、辺が存在するとき
			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
				}
			}
		}
	}

	sum := 0
	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += M[i][p[i]]
		}
	}
	return sum
}

func main() {
	sc.Split(bufio.ScanWords)
	n = nextInt()

	for i := 0; i < n; i++ {

		for j := 0; j < n; j++ {
			tmp := nextInt()
			if tmp == -1 {
				tmp = INFTY
			}
			M[i][j] = tmp
		}

	}

	fmt.Println(prim())

}

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, a[MAX][MAX];

int prim(){
  int u, min;
  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){
    min = INFTY;
    u = -1;
    for(int i=0;i<n;i++){
      if(min > d[i] && color[i] != BLACK){
	u = i;
	min = d[i];
      }
    }
    if(u == -1)break;
    color[u] = BLACK;
    for(int v=0;v<n;v++){
      if(color[v] != BLACK && a[u][v] != INFTY){
	if(d[v]>a[u][v]){
	  d[v] = a[u][v];
	  p[v] = u;
	  color[v] = GRAY;
	}
      }

    } //end of (for)

  } // end of while
  int sum = 0;
  for(int i=0;i<n;i++){
    if(p[i] != -1) sum += a[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;
      a[i][j] = (e == -1) ? INFTY : e;
    }
  }
  
  cout << prim() <<endl;
  
  return 0;
}

C++: #include <stdio.h>
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 d[n], p[n];
    int color[n];
    
    for(int i=0; i<n; i++) {
        color[i] = WHITE;
        d[i] = INFTY;
        p[i] = -1;
    }
    
    d[0] = 0;
    
    int sum = 0;
    
    while(1) {
        int u;
        int mincost = INFTY;
        for (int i=0; i<n; i++) {
            if (color[i] != BLACK && d[i] < mincost) {
                mincost = d[i];
                u = i;
            }
        }
        
        if (mincost == INFTY) break;
        
        color[u] = BLACK;
        
        int tmp = -1;
        for (int v=0; v<=n; v++) {
            if (color[v] != BLACK && M[u][v] != INFTY) {
                if(M[u][v] < d[v]) {
                    d[v] = tmp = M[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
        if(tmp != -1) sum += tmp;
    }

    return sum;
}

int main() {
    scanf("%d", &n);
    for (int i=0; i<n; i++) {
        for (int j=0; j<n; j++) {
            int tmp;
            scanf("%d", &tmp);
            M[i][j] = (tmp == -1) ? INFTY : tmp;
        }
    }
    
    int sum = prim();
    printf("%d\n", sum);
    
    return 0;
}

C++: #include<iostream>
#include<utility>
#include<algorithm>
using namespace std;
int matrix[100][100];
pair<int,int> edges[10010];
int cost[10010];
int src[10010];
int dst[10010];
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 <bits/stdc++.h>

using namespace std;

#define FOR(i,s,e) for((i)=(s);(i)<(int)(e);(i)++)
#define REP(i,e) FOR(i,0,e)

#define all(o) (o).begin(), (o).end()
#define psb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))

typedef long long ll;
typedef pair<int, int> PII;

const double EPS = 1e-10;

const int INF = 1000 * 1000 * 1000;
const int N = 100;
int n;
int c[N][N];
int d[N];
bool used[N];

int prim() {
  int i, res = 0;
  for (i=0; i<n; i++) {
    d[i] = INF;
    used[i] = false;
  }

  d[0] = 0;
  while (1) {
    int v = -1;
    for (i=0; i<n; i++)
      if (!used[i] && (v==-1 || (v>=0 && d[i]<d[v])))
        v = i;
  
    if (v==-1) break;
    used[v] = true;
    res += d[v];
    for (i=0; i<n; i++)
      d[i] = min(d[i], c[v][i]);
  }

  return res;
}

int main() {
  int i, j;
  scanf("%d ", &n);
  for (i=0; i<n; i++)
    for (j=0; j<n; j++) {
      scanf("%d ", &(c[i][j]));
      if (c[i][j]==-1) c[i][j] = INF;
    }
  printf("%d\n", prim());
  return 0;
}