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 <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < n; i++)
#define repp(i, m, n) for(int i = m; i < n; i++)
const int    INF = 100000000;
const double EPS = 1e-10;
const int    MOD = 1000000007;
using namespace std;
typedef long long ll;
typedef pair<int, int> pai;
typedef pair<ll,ll> pal;
int e[101][101];
int t;
pai edge[10001];
int c[10001];
int sz[10001];
int n;
int P[10001];
int ans;
int x, y;
void init(int k)
{
    repp(i, 1, k+1)
    {
        P[i]=i;
        sz[i]=1;
    }
}
int root(int a)
{
    if(P[a]==a)
    {
        return a;
    }
    else
    {
        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)
{
    if(sz[root(a)]<sz[root(b)])
    {
        swap(a, b);
    }
    sz[root(a)]+=sz[root(b)];
    P[root(b)]=root(a);
}
int main()
{
    cin >> n;
    rep(i, n)
    {
        rep(j, n)
        {
            cin >> e[i+1][j+1];
        }
    }
    t=0;
    rep(i, n)
    {
        repp(j, i+1, n)
        {
            if((i<j)&&(e[i+1][j+1]!=-1))
            {
                edge[t]=make_pair(e[i+1][j+1]*1000+i+1, j+1);
                //cout << edge[t].first << ' ' << j+1 << ' ' << t << endl;
                t++;
            }
        }
    }
    sort(edge, edge+t);
    //rep(i, t)
    //{
    //	cout << edge[i].first << ' ' << edge[i].second << endl;
    //}
    rep(i, t)
    {
        c[i]=edge[i].first / 1000;
        edge[i]=make_pair(edge[i].first%1000, edge[i].second);
        // cout << c[i] << ' ' << edge[i].first << ' ' << edge[i].second << endl;
    }
    init(n);
    ans=0;
    rep(i, t)
    {
    if(!is_same_set(edge[i].first, edge[i].second))
        {
            unite(edge[i].first, edge[i].second);
            ans+=c[i];
            // cout << edge[i].first << ' ' << edge[i].second << ' ' << i << ' ' << ans << endl;
        }
    }
    cout << ans << endl;
    return 0;
}

C++: #include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define N 105
int matrix[N][N];
//http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_12_A
//spanning tree tree
bool power[N]; // start from 1;
int main(){
	int n;
	scanf("%d",&n);
	memset(matrix, 0,sizeof(matrix));
	memset(power,0,sizeof(power));
	for(int i = 1; i<=n; i++){
		for(int j = 1; j<=n; j++){
			scanf("%d",&matrix[i][j]);//-1 means nothing
		}
	}
	int count = 0;
	int res = 0;
	int min = 2005;
	while(count<n-1){
		//find minmila ele from matrix
		int v1 = 0,v2 = 0;
		min = 2005;
		for(int i = 1; i<=n;i++){
			for(int j = 1;j<=n; j++){
				if(matrix[i][j]!=-1 && matrix[i][j]<min){
					if(count==0){
						if(power[i] == 0 && power[j]==0) {
							v1 = i;v2 = j;
							//printf("i:%d j:%d\n",i,j);
							min = matrix[i][j];
						}
						//continue;
					}else {
							if((power[i] == 1 && power[j]==0)||(power[i] == 0 && power[j]==1)){
							v1 = i;v2 = j;
							min = matrix[i][j];
						}
					}
					
				}
			}
		}
		//printf("min:%d\n",min);
		matrix[v1][v2] = -1;
		power[v1] = 1;
		power[v2] = 1;
		res+=min;
		count++;
	}
	printf("%d\n",res);
	return 0;
}

C++: /*#include<iostream>
#include<algorithm>
#include<stack>
#include<queue>
using namespace std;
int main(){
	int n, a, sum = 0;
	int temp = 1000000;
	int n1, n2;
	int r1[101] = {0}, r2[101] = { 0 };
	int m[101][101] = { 0 };
	cin >> n;
	for (int i = 0; i < n; i++){
		for (int l = 0; l < n; l++){
			cin >> a;
			m[i][l] = a;
		}
	}
	for (int i = 0; i < n-1; i++){
		for (int l = 0; l < n; l++){
			cout << m[i][l] << "   " << i <<endl;

			if (m[i][l] == -1) continue;
			if (m[i][l] < temp&&r1[l] == 0 && r2[i] == 0){
				temp = m[i][l];
				n1 = i; n2 = l;
			}
		}
		if (temp != 1000000){
			sum += temp;
			cout << i + 1 << endl;
			cout << temp <<endl;
			r1[n1] = -1; r2[n2] = -1;
			cout << n1  << n2 << endl;
			n1 = 0; n2 = 0;
			temp = 1000000;
		}
	}
	cout << sum << endl;
	return 0;
}*/
/*
5
-1 2 3 1 -1
2 -1 -1 4 -1
3 -1 -1 1 1
1 4 1 -1 3
-1 -1 1 3 -1
*/
#include<queue>
#include<stack>
#include<vector>
#include<iostream>
#include<algorithm>
using namespace std;
#define WHITE 0
#define BLACK 1
#define GRAY 2
#define INFTY 1000000
int color[101];
int m[101][101];
int d[101];
int p[101];
int mincost = INFTY;
int n;
int yy;


void prim(int u){
	while (1){
		mincost = INFTY;
		for (int i = 0; i < n - 1; i++){
			if (color[i] != BLACK&&d[i] < mincost){
				mincost = d[i];
				u = i;
			}
		}
		if (mincost == INFTY) break;
		color[u] = BLACK;
		for (int v = 0; v < n - 1; v++){
			if (color[v] != BLACK&&m[u][v] != INFTY){
				if (m[u][v] < d[v]){
					d[v] = m[u][v];
					p[v] = u;
					color[v] = GRAY;
				}
			}
		}
	}
}
int main(){
	int a[10] = { 0 };
	for (int i = 0; i < 101; i++){
		color[i] = INFTY; d[i] = INFTY; p[i] = -1;
	}
	for (int i = 0; i < 101; i++){
		for (int l = 0; l < 101; l++){
			m[i][l] = 0;
		}
	}
	cin >> n;
	for (int i = 0; i < n; i++){
		for (int l = 0; l < n; l++){
			cin >> m[i][l];
		}
	}
	prim(0);
	int sum = 0;
	for (int i = 0; i < n; i++){
		sum += p[i];
	}
	cout << sum*(-1) << endl;
	return 0;
}