Go: package main

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

const (
	MAX_N      = 200
	MAX_WEIGHT = 2000
)

type Edge struct {
	start  int
	end    int
	weight int
}

type ShortestInfo struct {
	edges    []Edge
	shortest int
}

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

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

	shortestList := make([]ShortestInfo, n)
	for i := 1; i < n; i++ {
		shortestList[i] = ShortestInfo{edges: []Edge{}, shortest: MAX_N*MAX_WEIGHT + 1}
	}

	adjacentMatrix := make([][]int, n)
	for i := 0; i < n; i++ {
		adjacentMatrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			v, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			adjacentMatrix[i][j] = v
		}
	}

	mst([]int{1}, shortestList, adjacentMatrix)
	fmt.Println(calculateMinWeight(shortestList))
}

func calculateMinWeight(shortestList []ShortestInfo) int {
	visitedList := make([]bool, len(shortestList))
	visitedList[0] = true
	sumWeight := 0
	for !visitedAll(visitedList) {
		shortestInfo := shortestList[0]
		shortestList = shortestList[1:]
		edges := shortestInfo.edges
		for _, edge := range edges {
			if !visitedList[edge.end-1] {
				visitedList[edge.end-1] = true
				sumWeight += edge.weight
			}
		}
	}
	return sumWeight
}

func visitedAll(visitedList []bool) bool {
	for _, v := range visitedList {
		if !v {
			return false
		}
	}
	return true
}

func mst(nodeStack []int, shortestList []ShortestInfo, adjacentMatrix [][]int) {
	for len(nodeStack) > 0 {
		currentNode := nodeStack[0]
		nodeStack = nodeStack[1:]
		currentShortest := getShortest(currentNode, shortestList)
		adjacents := findAdjacents(currentNode, adjacentMatrix)
		for i := 0; i < len(adjacents); i++ {
			adj := adjacents[i]
			s := getShortest(adj.end, shortestList)
			if currentShortest.shortest+adj.weight < s.shortest || (currentShortest.shortest+adj.weight == s.shortest && len(currentShortest.edges)+1 > len(s.edges)) {
				setShortest(adj.end, adj, currentShortest, shortestList)
				nodeStack = append(nodeStack, adj.end)
			}
		}
	}
}

func getShortest(node int, shortestList []ShortestInfo) ShortestInfo {
	return shortestList[node-1]
}

func setShortest(node int, edge Edge, currentShortest ShortestInfo, shortestList []ShortestInfo) {
	newEdges := make([]Edge, len(currentShortest.edges)+1)
	for i := 0; i < len(newEdges)-1; i++ {
		newEdges[i] = currentShortest.edges[i]
	}
	newEdges[len(newEdges)-1] = edge
	shortestInfo := ShortestInfo{edges: newEdges, shortest: currentShortest.shortest + edge.weight}
	shortestList[node-1] = shortestInfo
}

func findAdjacents(currentNode int, adjacentMatrix [][]int) []Edge {
	adjacents := adjacentMatrix[currentNode-1]
	edges := []Edge{}
	for i, v := range adjacents {
		if v > 0 {
			edges = append(edges, Edge{start: currentNode, end: i + 1, weight: v})
		}
	}
	return edges
}

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

C++: #include <stdio.h>
#include <stdlib.h>
#define MAX 101
#define rep(i,n) for(int i=0;i<n;i++)
#define infinity 1e9
typedef struct tuple{
    int a;
    int b;
    int w;
}tuple;
int n,t=0,cost=0;
int G[MAX][MAX],tags[MAX];
tuple v[5010];
int cmpAscW(const void * n1, const void * n2){
    if (((tuple *)n1)->w > ((tuple *)n2)->w)return 1;
	else if (((tuple *)n1)->w < ((tuple *)n2)->w)return -1;
	else return 0;
}
int min(int x,int y){
    if(x < y)return x;
    else return y;
}
int max(int x,int y){
    if(x<y)return y;
    else return x;
}
void Kruskal(){
    int m,temp=0;
    rep(i,t){
        if(tags[v[i].a] != tags[v[i].b]){
            temp = max(tags[v[i].a],tags[v[i].b]);
            m = min(tags[v[i].a],tags[v[i].b]);
            tags[v[i].a] = m;
            tags[v[i].b] = m;
            cost += v[i].w;
            for(int j=m;j<n;j++){
                if(tags[j] == temp)tags[j]=m;
            }
        }
    }
}
int main(){
    scanf("%d",&n);
    rep(i,5010){
        v[i].w = infinity;
    }
    rep(i,n){
        tags[i] = i;
        rep(j,n){
            scanf("%d",&G[i][j]);
            if(i<j){
                if(G[i][j] != -1){
                    v[t].a = i;
                    v[t].b = j;
                    v[t].w = G[i][j];
                    t++;
                }
            }
        }
    }
    qsort(v, t, sizeof(tuple), cmpAscW);
    Kruskal();
    printf("%d\n",cost);
    return 0;
}

C++: 
#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
using namespace std;
int P[1010];
int cost[5000];
int src[5000];	
int dst[5000];
int A[100 + 10][100 + 10];
int M = 0;
vector< pair<int,int> > edges;

void init(int N)
{
    for(int i = 1; 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()
{
	int n = 0;
	cin >> n; 
	for(int r = 0; r < n; ++r)
	{
		for(int c = 0; c < n; ++c)
		{
			cin >> A[r][c];
		}
	}
	for (int r = 0; r < n; ++r)
	{
		for(int c = r + 1; c < n; ++c)
		{
			if(A[r][c] > -1)
			{
				cost[M] = A[r][c];
				src[M] = r;
				dst[M] = c;
				edges.push_back(make_pair(cost[M],M));
				M += 1;
			}
		}
	}
	sort(edges.begin(),edges.end());
	int sum = 0;
	init(n);
	for(int i = 0; i < M; ++i)
	{
		if(is_same_set(src[edges[i].second], dst[edges[i].second]) == 1) continue;
			unite(dst[edges[i].second],src[edges[i].second]);
			sum += edges[i].first;
	}
	cout << sum << endl;
}

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]=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;
}