Go: package main

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

// Define disjoint-set forests

type vertexNo int

type vertex struct {
	number vertexNo
	rank int
	parent *vertex
}

func makeSet(number vertexNo) vertex {
	return vertex {
		number: number,
		rank: 0,
		parent: nil,
	}
}

func union(x, y *vertex) *vertex {
	return link(findSet(x), findSet(y))
}

func link(x, y *vertex) *vertex {
	if x.rank > y.rank {
		y.parent = x
		return x
	} else {
		x.parent = y
		if x.rank == y.rank {
			y.rank += 1
		}
		return y
	}
}

func findSet(v *vertex) *vertex {
	if v.parent == nil {
		return v
	}
	v.parent = findSet(v.parent)
	return v.parent
}

// Function to calculate minimum spanning tree

type matrix [][]int

type edge struct {
	one vertexNo
	two vertexNo
	weight int
}

const(
	MAX_VERTICES = 100
)

func newEdgesFromMatrix(matrix matrix) []edge {
	edges := make([]edge, 0, MAX_VERTICES * MAX_VERTICES)

	for i := 0; i < len(matrix); i++ {
		row := matrix[i]
		for j := i; j < len(row); j++ {
			if row[j] >= 0 {
				edge := edge{one: vertexNo(i+1), two: vertexNo(j+1), weight: row[j]}
				edges = append(edges, edge)
			}
		}
	}

	return edges
}

func solve(matrix matrix) int {
	nVertices := len(matrix)

	// initialize vertices
	vertices := make([]vertex, nVertices)
	for i := 0; i < nVertices; i++ {
		vertices[i] = makeSet(vertexNo(i+1))
	}

	// prepare edges sorted in the ascending order of weight
	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	unionCount := 0
	weightSum := 0
	for unionCount < nVertices-1 {
		for i := 0; i < len(edges); i++ {
			edge := edges[i]
			v1 := &vertices[edge.one-1]
			v2 := &vertices[edge.two-1]
			rep1 := findSet(v1)
			rep2 := findSet(v2)
			if rep1.number == rep2.number {
				continue
			}
			union(rep1, rep2)
			edges = append(edges[0:i], edges[i+1:]...)
			weightSum += edge.weight
			unionCount++
			break
		}
	}

	return weightSum
}

// main

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	matrix := parseMatrix(n, sc)

	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	fmt.Println(solve(matrix))
}

func parseMatrix(n int, sc *bufio.Scanner) [][]int {
	matrix := make([][]int, n)
	for i := 0; i < n; i++ {
		matrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			x, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			matrix[i][j] = x
		}
	}
	return matrix
}

func nextText(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextInt(sc *bufio.Scanner) (int, error) {
	return strconv.Atoi(nextText(sc))
}

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

int n, M[100][100];

int prim()
{
	int i,u,v,min_v,sum;
	int d[100],p[100],c[100];
	
	for(i=0;i<=n-1;i++)
	{
		d[i]=(1<<21);
		p[i]=-1;
		c[i]=0;
	}
	
	d[0]=0;
	
	while(1)
	{
		min_v=(1<<21);
		u=-1;
		for(i=0;i<=n-1;i++)
		{
			if(min_v > d[i] && c[i] != 2)
			{
				u=i;
				min_v=d[i];
			}
		}
		if(u==-1) break;
		c[u]=2;
		for(v=0;v<=n-1;v++)
		{
			if(c[v] != 2 && M[u][v] != (1<<21))
			{
				if(d[v] > M[u][v])
				{
				    d[v]=M[u][v];
				    p[v]=u;
				    c[v]=1;
				}
			}
		}
	}
	sum=0;
	for(i=0;i<=n-1;i++)
	{
		if(p[i] != -1) sum+=M[i][p[i]];
	}
	return sum;
}

int main()
{
	int i,j,e;
	cin >> n;
	
	for(i=0;i<=n-1;i++)
	{
		for(j=0;j<=n-1;j++)
		{
			cin >> e;
			if(e == -1) M[i][j]=(1<<21);
			else M[i][j]=e;
		}
	}
	
	cout << prim() << endl;
	return 0;
}

C++: #include <iostream>
#include <cstdio>
using namespace std;
static const int  N = 100;
static const int  INFTY = (1<<21);
int M[N][N], color[N];
int n, d[N], p[N];
int ans = 0;

int prim()
{
    for (int i = 0; i < n; i++)
    {
        color[i] = -1;
        d[i] = INFTY;
        p[i] = -1;
    } 
    d[0] = 0;
    int u = -1;
    while (true)
    { 
        int mincost = INFTY;
        u = -1;
        for (int i = 0; i < n; i++)
        {
            if (color[i] != 2 && d[i] < mincost)
            { 
                mincost = d[i];
                u = i;
            }  
        } 

        if (mincost == INFTY) break;
        color[u] = 2;
        for (int i = 0; i < n; i++)
        {
            if (color[i] != 2 && M[u][i] != INFTY)
            { 
                if (M[u][i] < d[i])
                { 
                    d[i] = M[u][i];
                    p[i] = u;
                    color[i] = 1;
                }  
            }  
        } 
    }

    for (int i = 0; i < n; i++)
    {
        if (color[i] == 2 && p[i] != -1) ans += M[i][p[i]];

    } 
    return ans;
}

int main()
{
    cin>>n;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            int a;
            cin>>a;
            if(a != -1) M[i][j] = a;
            else M[i][j] = INFTY;
        }  
    } 
    prim();
    cout<<ans<<endl;    
    return 0;
}

C++: #include<stdio.h>

static const int MAX = 500;
static const int INFTY = (1<<21);

main(){
  int n, i, j, e, sum,M[MAX][MAX]={0};
  int u,minV,INT_MAX,A[MAX]={INFTY},key[MAX]={INFTY};
  /*

    your code


   */

  scanf("%d", &n);
  
  for ( i = 0; i< n; i++ ){
    for ( j = 0; j < n; j++ ){
      scanf("%d", &e);
      M[i][j] = (e==-1)?INFTY:e;
    }
  }
  
  
  while(){
    minV = 
      for(i=1;i<=n;i++){
        if((i < minV) && 

  






















  sum = 0;

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

  printf("%d\n", sum);

  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;
typedef long long ll;

static const int INF = 1e9;
static const int MAX = 100;

int n;
struct edge{int to, cost;};
typedef pair<int, int> P;

int mincost[MAX];
bool used[MAX];
vector< vector<edge> > A(MAX);

int prim(){
    int to, cost, res = 0;
    priority_queue<P, vector<P>, greater<P>> que;
    fill(mincost, mincost + n, INF);
    fill(used, used + n, false);
    mincost[0] = 0;
    que.push(P(0, 0));

    while(!que.empty()){
        P p = que.top(); que.pop();
        if (used[p.second]) continue;
        used[p.second] = true;

        for (int i = 0; i < A[p.second].size(); i++){
            to = A[p.second][i].to;
            cost = A[p.second][i].cost;
            if (used[to]) continue;
            if (mincost[to] > cost){
                mincost[to] = cost;
                que.push(P(mincost[to], to));
            }
        }
    }
    for (int i = 0; i < n; i++) res += mincost[i];
    return res;
}

int main(){
    cin >> n;
    edge x;
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            scanf("%d", &x.cost);
            x.to = j;
            if (x.cost != -1) A[i].push_back(x);
        }
    }
    cout << prim() << endl;
    return 0;
}