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<stdio.h>

#define INFTY (1<<21)
#define MAX 100
#define WHITE 0
#define GRAY 1
#define 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] = GRAY;
	 }
       }
    }
  }
  int sum = 0;
  for(int i = 0; i < n; i++){
    if(p[i] != -1)sum += M[i][p[i]];
  }

  return sum;
}

int main(){
  
  scanf("%d",&n);

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

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

  return 0;
}

C++: #include <tuple>
#include <iostream>
#include <algorithm>
using namespace std;
int P[10010]; 
tuple<int,int,int> a[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(void){
    int n,value;
    cin >> n;
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            cin >> value;
            a[n*i+j] = make_tuple(value,i,j);
        }
    }
    init(n*n);
    sort(a,a+n*n);
    int sum =0;
    int x,y;
    for(int i =0;i<n*n;i++){
        x = get<1>(a[i]);
        y = get<2>(a[i]);
        if(is_same_set(x,y)!=1){
            if(get<0>(a[i])!=-1){
                sum += get<0>(a[i]);
                unite(x,y);
            }
        }
    }
    cout << sum << endl;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>

int color(std::vector<std::vector<int> > v) {
	std::vector<int> color(v.size(), 0);
	int count = 0, color_count = 1;
	for (int i = 0; i <= 2000; i++) {
		for (size_t j = 0; j < v.size(); j++) {
			for (size_t k = j + 1; k < v.size(); k++) {
				if (v[j][k] == i && ((color[k] == 0 || color[j] == 0) || (color[k] != color[j]))) {
					if (color[k] == 0) {
						if (color[j] != 0) {
							color[k] = color[j];
						} else {
							color[k] = color[j] = color_count;
							color_count++;
						}
					} else {
						if (color[j] == 0) {
							color[j] = color[k];
						} else {
							int num = color[j];
							std::replace(color.begin(), color.end(), num, color[k]);
						}
					}
					count += i;
				}
			}
		}
	}
	return count;
}

int main() {
	int num;
	std::cin >> num;

	std::vector<std::vector<int> > v(num);

	for (int i = 0; i < num; i++) {
		for (int j = 0; j < num; j++) {
			int n;
			std::cin >> n;
			v[i].push_back(n);
		}
	}

	std::cout << color(v) << std::endl;

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
const int MAXN = 100+7;
const int INF = 2e3+7;
int m[MAXN][MAXN];
int sum;
set<int> notin;
set<int> isin;
bool visit[MAXN];
void printset(set<int> r)
{

    for(set<int>::iterator it = r.begin(); it != r.end(); it++)
    {
        printf("%d,", *it);
    }
    printf("\n");
}
void prim(int root)
{
    isin.insert(root);
    notin.erase(root);
    visit[root] = true;
    while(!notin.empty())
    {
        int u;
        int min_e = INF;
        for(set<int>::iterator it = isin.begin(); it!=isin.end(); it++)
        {
            int r = *it;
            int i;
            for(set<int>::iterator it2 = notin.begin(); it2!=notin.end(); it2++)
            {
                int h = *it2;
                if(m[h][r]<min_e && m[h][r]!=-1 && visit[h] == false)
                {
                    min_e = m[h][r];
                    u = h;
                }

            }
        }
        isin.insert(u);
        notin.erase(u);
        visit[u] = true;
        sum+=min_e;
    }
}
int main()
{
//    freopen("../in.txt", "r", stdin);
    memset(visit, false, sizeof(visit));
    int n;
    scanf("%d", &n);
    int i, j;
    for(i = 0; i < n; i++)
    {
        for(j = 0; j < n; j++)
        {
            scanf("%d", &m[i][j]);
        }
        notin.insert(i);

    }
    sum = 0;
    prim(0);
    printf("%d\n", sum);
    return 0;
}