Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

C++: #include <stdio.h>
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 d[n], p[n];
    int color[n];
    
    for(int i=0; i<n; i++) {
        color[i] = WHITE;
        d[i] = INFTY;
        p[i] = -1;
    }
    
    d[0] = 0;
    
    int sum = 0;
    
    while(1) {
        int u;
        int mincost = INFTY;
        for (int i=0; i<n; i++) {
            if (color[i] != BLACK && d[i] < mincost) {
                mincost = d[i];
                u = i;
            }
        }
        
        if (mincost == INFTY) break;
        
        color[u] = BLACK;
        
        int tmp = -1;
        for (int v=0; v<=n; v++) {
            if (color[v] != BLACK && M[u][v] != INFTY) {
                if(M[u][v] < d[v]) {
                    d[v] = tmp = M[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
        if(tmp != -1) sum += tmp;
    }

    return sum;
}

int main() {
    scanf("%d", &n);
    for (int i=0; i<n; i++) {
        for (int j=0; j<n; j++) {
            int tmp;
            scanf("%d", &tmp);
            M[i][j] = (tmp == -1) ? INFTY : tmp;
        }
    }
    
    int sum = prim();
    printf("%d\n", sum);
    
    return 0;
}

C++: #include<iostream>
#include<utility>
#include<algorithm>
using namespace std;
int matrix[100][100];
pair<int,int> edges[10010];
int cost[10010];
int src[10010];
int dst[10010];
int p[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()
{
    int n,amount=0,sum=0;
    
    cin>>n;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cin>>matrix[i][j];
        }
    }
    
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<=i;j++)
        {
            if(matrix[i][j]!=-1)
            {
                cost[amount]=matrix[i][j];
                src[amount]=i;
                dst[amount]=j;
                amount++;
            }
        }
    }
    for(int i=0;i<amount;i++)
    {
        edges[i]=make_pair(cost[i],i);
    }

	init(n);
    
    sort(edges,edges+amount);
    
    for(int i=0;i<amount;i++)
    {
        if(is_same_set(src[edges[i].second],dst[edges[i].second]))
			continue;
		unite(src[edges[i].second],dst[edges[i].second]);
		sum+=edges[i].first;
    }
	cout<<sum<<endl;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define FOR(i,s,e) for((i)=(s);(i)<(int)(e);(i)++)
#define REP(i,e) FOR(i,0,e)

#define all(o) (o).begin(), (o).end()
#define psb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))

typedef long long ll;
typedef pair<int, int> PII;

const double EPS = 1e-10;

const int INF = 1000 * 1000 * 1000;
const int N = 100;
int n;
int c[N][N];
int d[N];
bool used[N];

int prim() {
  int i, res = 0;
  for (i=0; i<n; i++) {
    d[i] = INF;
    used[i] = false;
  }

  d[0] = 0;
  while (1) {
    int v = -1;
    for (i=0; i<n; i++)
      if (!used[i] && (v==-1 || (v>=0 && d[i]<d[v])))
        v = i;
  
    if (v==-1) break;
    used[v] = true;
    res += d[v];
    for (i=0; i<n; i++)
      d[i] = min(d[i], c[v][i]);
  }

  return res;
}

int main() {
  int i, j;
  scanf("%d ", &n);
  for (i=0; i<n; i++)
    for (j=0; j<n; j++) {
      scanf("%d ", &(c[i][j]));
      if (c[i][j]==-1) c[i][j] = INF;
    }
  printf("%d\n", prim());
  return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <math.h>
#include <map>
#include <functional>
#include <iomanip>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <typeinfo>
#define PI 3.14159265359
#define INF 99999999;
#define rep(i, n) for(int i=0; i<n; i++)
#define REP(n) rep(i, n)
#define EPS 1e-10
typedef long long ll;
using namespace std;
typedef pair<int, int> P;

double distanceAB(double xa, double ya, double xb, double yb);
//void trace(int A[], int N);

/*
class Target
{
public:
	vector <string> draw(int n)
	{

	}
};
*/


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];
	
	REP(n)
	{
		d[i] = INFTY;
		p[i] = -1;
		color[i] = WHITE;
	}
	
	d[0] = 0;
	
	while (1)
	{
		minv = INFTY;
		u = -1;
		REP(n)
		{
			if (minv > d[i] && color[i] != BLACK)
			{
				u = i;
				minv = d[i];
			}
		}
		if (u == -1) break;
		color[u] = BLACK;
		rep(v, n)
		{
			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;
	REP(n)
	{
		if (p[i] != -1) sum += M[i][p[i]];
	}
	
	return sum;
}


int main()
{
	cin >> n;
	
	rep(i, n)
	{
		rep(j, n)
		{
			int e;
			cin >> e;
			M[i][j] = (e == -1) ? INFTY : e;
		}
	}
	
	cout << prim() << endl;
	
	return 0;
}


/*
void trace(int A[], int N)
{
	REP(N)
	{
		if (i > 0) cout << " ";
		cout << A[i];
	}
	cout << endl;
}
*/


double distanceAB(double xa, double ya, double xb, double yb)
{
	return sqrt((xb-xa)*(xb-xa) + (yb-ya)*(yb-ya));
}