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++: //最小全域木をプリム法で求める。
//計算量O(v^2) (vは頂点の数)

#include <bits/stdc++.h>
using namespace std;

#define MAX 105
#define INFTY 10000000
#define WHITE 0
#define GRAY 1
#define BLACK 2

//Mは隣接行列
int n, M[MAX][MAX];

int prim(){
    int u, minv;
    int d[MAX], p[MAX], color[MAX];

    for(int i=1; i<=n; i++){
        d[i] = INFTY;
        p[i] = -1;
        color[i] = WHITE;
    }

    d[1] = 0;

    while(1){
        minv = INFTY;
        u = -1;
        for(int i=1; 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=1; 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=1; i<=n; i++){
        if(p[i] != -1) sum += M[i][p[i]];
    }

    return sum;
}

int main(){
    cin >> n;

    for(int i=1; i<=n; i++){
        for(int j=1; j<=n; j++){
            int e;
            cin >> e;
            if(e == -1){
                M[i][j] = INFTY;
            }else{
                M[i][j] = e;
            }
        }
    }

    cout << prim() << endl;

    return 0;
}

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

#define INF 1000000

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

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

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(true)
    {
        minv = INFTY;
        u = -1;
        for (int i = 0; i < n; i++)
        {
            if (color[i] != BLACK && d[i] < minv)
            {
                minv = d[i];
                u = i;
            }
        }
        if (u == -1) break;
        color[u] = BLACK;
        for (int v = 0; v < n; v++)
        {
            if (color[v] != BLACK && M[u][v] != INFTY)
            {
                if ( M[u][v] < d[v])
                {
                    d[v] = M[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }
    int s = 0;
    for (int i = 0; i < n; i++)
    {
        if (p[i] != -1)
        {
            s += M[i][p[i]];
        }
    }
    return s;
}

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;
}