Go: package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

C++: #include<bits/stdc++.h>
using namespace std;
int n,M[105][105];
int prim(){
  int u,minv;
  int d[105],p[105],color[105];
  for(int i=0;i<n;i++){
    d[i]=1234567890;
    p[i]=-1;
    color[i] = 0;
  }
  d[0]=0;
  while(1){
    minv = 1234567890;
    u = -1;
    for(int i=0;i<n;i++){
      if(minv > d[i] && color[i]!=2){
	u=i;
	minv = d[i];
      }
    }
    if(u==-1)break;
    color[u]=2;
    for(int v=0;v<n;v++){
      if(color[v]!=2&&M[u][v]!=1234567890){
	if(d[v]>M[u][v]){
	  d[v]=M[u][v];
	  p[v]=u;
	  color[v]=1;
	}
      }
    }
  }
  int sum = 0;
  for(int i=0;i<n;i++){
    if(p[i]!=-1)sum+=M[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;
      M[i][j]=(e==-1)? 1234567890 : e;
    }
  }
  cout << prim() << endl;
  return 0;
}

C++: #include <stdio.h>

const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;
const int N = 100;
const int INF = 2000000000;

int g[N + 1][N + 1];
int d[N + 1], p[N + 1], color[N + 1];
int n;

void prim()
{
	for (int i = 1; i <= n; i++)
	{
		color[i] = WHITE;
		d[i] = INF;
		p[i] = -1;
	}
	d[1] = 0;

	while (true)
	{
		int min = INF;
		int u = -1;
		for (int i = 1; i <= n; i++)
		{
			if (color[i] != BLACK && d[i] < min)
			{
				min = d[i];
				u = i;
			}
		}
		if (u == -1)
			break;

		color[u] = BLACK;

		for (int i = 1; i <= n; i++)
		{
			if (color[i] != BLACK && g[u][i] != INF && d[i] > g[u][i])
			{
				d[i] = g[u][i];
				color[i] = GRAY;
				p[i] = u;
			}
		}
	}
	int sum = 0;
	for (int i = 1; i <= n; i++)
	{
		if (p[i] != -1)
			sum += g[p[i]][i];
	}
	printf("%d\n", sum);
}

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

	return 0;
}

C++: #include<bits/stdc++.h>
#define INF 0x3f3f3f3f
using namespace std;
const int MAXN = 105;

int m[105][105];
int n,e;

int prim(int s)
{
    int minv,cnt[MAXN],k,ans = 0;
    for(int i = 1; i <= n; ++i)
        cnt[i] = m[s][i];
    cnt[s] = 0;
    for(int i = 1; i < n; ++i)
    {
        minv = INF;
        for(int j = 1; j <= n; ++j)
        {
            if(cnt[j] && cnt[j]<minv)
                minv = cnt[j],k = j;
        }
        cnt[k] = 0;
        ans += minv;
        for(int j = 1; j <= n; ++j)
            if(m[k][j] < cnt[j])
                cnt[j] = m[k][j];
    }
    return ans;
}

int main(void)
{
    cin>>n;
    for(int i = 1; i <= n; ++i)
    {
        for(int j = 1; j <= n; ++j)
        {
            cin>>e;
            m[i][j] = e==-1?INF:e;
        }
    }
    cout<<prim(1)<<'\n';
    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;

struct Node{
  int color, dist, 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;
    cout << " dist : " << node[i].dist << 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].dist = INFTY;
    node[i].parent = -1;
  }

  int p = 0;
  node[p].color = BLACK;
  node[p].dist = 0;

  while(true){
    Printnodes();

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

    int min_d = INFTY;
    p = -1;
    for(int i = 0; i < n; i++){
      if(node[i].dist < min_d && node[i].color != BLACK){
        min_d = node[i].dist;
        p = i;
      }
    }

    if(p == -1)
      break;

    node[p].color = BLACK;
    cout << "node " << p << " turns to BLACK!" << endl;
    cout << "Total distance is " << totaldist << endl;
  }

  int sum = 0;

  for(int i = 0; i < n; i++){
    if(node[i].parent >= 0)
      sum += M[i][node[i].parent];
  }
  cout << sum << 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 (1) {
		minv = INFTY;
		u = -1;
		for (int i = 0; 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 = 0; 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] = u;
					color[v] = GRAY;
				}
			}
		}
	}
	int sum = 0;
	for (int i = 0; i < n; i++) {
		if (p[i] != -1)sum += M[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;
			M[i][j] = (e == -1) ? INFTY : e;
		}
	}

	cout << prim() << endl;

	return 0;
}