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 <vector>
#include <algorithm>
using namespace std;
bool f[100];
int n;
int tr[100];


int trmin(){
  int res=10000,resi;
  for(int i=0;i<n;i++)
    if(f[i]==0 && tr[i]<res) res = tr[i],resi=i;
  return resi;
}


int main (){

  int mp[100][100];

  cin >> n;
  for(int i=0;i<n;i++)
    for(int j=0;j<n;j++)
      cin >> mp[i][j];

  for(int i=0;i<n;i++) f[i]=0;
  for(int i=0;i<n;i++) tr[i]=10000;
  tr[0] = 0;
  int trsum=0;

  for(int k=0;k<n;k++){
    int r=trmin();
    f[r]=1;
    trsum+=tr[r];

    for(int i=0;i<n;i++) 
      if(mp[r][i]!=-1)
	tr[i] = min(tr[i],mp[r][i]);
  }
  cout<<trsum<<endl;

  return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define INF 2*1e9
int main(){
  
  int n;
  int cost[100][100];
  int mincost[100];
  int used[100]={};
  
  cin>>n;
  for(int i=0;i<n;i++){
    mincost[i]=INF;
    for(int j=0;j<n;j++){
      cin>>cost[i][j];
      if(cost[i][j]==-1)cost[i][j]=INF;
    }
  }

  mincost[0]=0;
  int ans=0;

  while(1){
    int v=-1;
    for(int u=0;u<n;u++){
      if(used[u]==0&&(v==-1||mincost[u]<mincost[v]))v=u;
    }
    
    if(v==-1)break;
    used[v]=1;
    ans+=mincost[v];
    
    for(int u=0;u<n;u++){
      mincost[u]=min(mincost[u],cost[v][u]);
    }
  }
  
  cout<<ans<<endl;
  
  return 0;
  
}

C++: #include<iostream>
using namespace std;
#define MAX 1000
#define Infty 10000

struct Edge{int cost, left, right; };

void Bubble(struct Edge A[], int N){
  for(int i=0;i<N;i++){
    for(int j=N-1;j>=i;j--){
      if(A[j].cost < A[j-1].cost){
        Edge buffa = A[j];
        A[j] = A[j-1];
        A[j-1] = buffa;
      }
    }
  }
}
void print(struct Edge A[], int N){
  for(int i=0;i<N;i++){
    cout << A[i].cost << A[i].left << A[i].right << endl;
  }
}

int find(int x, int parents[]){
  int c = x;
  while(parents[c]!=c) c = parents[c];
  return c;
}

void uunion(int x, int y, int parents[]){
  int a = find(x,parents);
  int b = find(y,parents);
  if(a!=b) parents[a] = b;
}

int main(){
    int n, M[MAX][MAX], d=0;
    int k = 0;
    struct Edge A[MAX];
    cin >> n;
    for(int i=0;i<n;i++){
      for(int j=0;j<n;j++){
        cin >> M[i][j];
        if(M[i][j]==-1) M[i][j] = Infty;
      }
    }
    for(int i=0;i<n;i++){
      for(int j=0;j<n;j++){
        if(j<i){
          //cout << "k = " << k << endl;
          A[k].cost = M[i][j];
          //cout << "M[1][1]=" << M[i][j] << endl;
          //cout << "A.cost = " << A[k].cost << endl;
          A[k].right = i;
          A[k].left = j;
          k++;
        }
      }
    }
    Bubble(A, k);
    
    int parents[k];
    for(int i=0;i<k;i++) parents[i] = i;
    for(int i=0;i<k;i++){
      if(find(A[i].left,parents)!=find(A[i].right,parents)){
        d += A[i].cost;
        uunion(A[i].left,A[i].right,parents);
      }
    }
    cout << d << 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;

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){
        if(node[i].dist > M[p][i]){
          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;
  }

  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;
}