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 <algorithm>
#include <vector>
#include <iostream>

typedef std::vector<int> TTree;
struct TPath
{
    int Id1;
    int Id2;
    int Cost;
    TPath(int AId1, int AId2, int ACost)
     : Id1(AId1), Id2(AId2), Cost(ACost)
    {}
};
bool Compare(const TPath& Left, const TPath& Right)
{
    if(Left.Cost  < 0) return false;
    if(Right.Cost < 0) return true;
    return Left.Cost < Right.Cost;
}


int main()
{
    int n;
    std::cin >> n;
    std::vector<TTree*> Table(n, NULL);
    for(std::size_t i = 0; i < n; ++i){
        Table[i] = new std::vector<int>(1, i);
    }
    std::vector<TPath> PathList;
    PathList.reserve(n*n);
    
    for(int i = 0; i < n; ++i){
        for(int j = 0; j < n; ++j){
            int Cost;
            std::cin >> Cost;
            PathList.push_back(TPath(i, j, Cost));
        }
    }
    std::sort(PathList.begin(), PathList.end(), Compare);
    
    int Total = 0;
    for(std::vector<TPath>::const_iterator It = PathList.begin();
        It != PathList.end(); ++It)
    {
        const TPath& Path = *It;
        TTree* Tree1 = Table[Path.Id1];
        TTree* Tree2 = Table[Path.Id2];
        if(Tree1 == Tree2){
            continue;
        }
        Tree1->insert(Tree1->end(), Tree2->begin(), Tree2->end());
        for(std::size_t j = 0; j < Tree2->size(); ++j){
            int Id = (*Tree2)[j];
            Table[Id] = Tree1;
        }
        delete Tree2;
        Total += Path.Cost;
        // std::cout << "[" << Path.Id1 << "]" << "[" << Path.Id2 << "] = " << Path.Cost << std::endl;
    }
    std::cout << Total << std::endl;
    return 0;
}

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

int root(int a,int P[])
{
    if(P[a] == a)
        return a;
    else    return (P[a] = root(P[a],P));
}
int is_same_set(int a,int b,int P[])
{
    return root(a,P) == root(b,P);
}

int main()
{
    int n,i,j,M=0,minsum=0;
    cin >> n;
    //init(n);
    int a[n][n],cost[n*n],src[n*n],dst[n*n];
    for(i=0;i<n;i++)
        for(j=0;j<n;j++)
            cin >> a[i][j];
    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;
                M++;
            }
    pair<int,int> edeges[M];
    int P[n];
    for(i=0;i<n;i++)
        P[i] = i;
    for(i=0;i<M;i++)
    {
        edeges[i].first = cost[i];
        edeges[i].second = i;
    }
    sort(edeges,edeges+M);
    for(i=0;i<M;i++)
    {
        if(is_same_set(src[edeges[i].second], dst[edeges[i].second], P))
            continue;
        else    {
                    P[root(src[edeges[i].second],P)] = root(dst[edeges[i].second],P);
                    minsum += edeges[i].first;
                }
    }
    cout << minsum << endl;
    return 0;
}

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

vector< vector < int > > adjMatrix;

int findMSTCost(int n) {
  vector< bool > visited (n, false);
  visited[0] = true;
  int cost = 0;
  for (int numberVertices = 1; numberVertices < n; numberVertices++) {
    int minEdge = 3000, minVertex = n;
    for (int i = 0; i < n; i++) {
      for (int j = 0; j < n; j++) {
	if ((i != j) &&
	    (visited[i] == true) &&
	    (visited[j] == false) &&
	    (adjMatrix[i][j] != -1) &&
	    (adjMatrix[i][j] < minEdge)) {
	  minEdge = adjMatrix[i][j];
	  minVertex = j;
	}
      }
    }
    cost += minEdge;
    visited[minVertex] = true;
  }
  return cost;
}

int main(int argc, char **argv) {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  adjMatrix = vector< vector < int > > (n, vector< int > (n, 0));
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      cin >> adjMatrix[i][j];
  cout << findMSTCost(n) << endl;
  return 0;
}