Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

const INF = 1 << 60

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < N; i++ {
		G[i] = make([]int, N)
		for j := 0; j < N; j++ {
			G[i][j] = sc.nextInt()
		}
	}
	d := make([]int, N)
	for i := 0; i < N; i++ {
		d[i] = INF
	}
	seen := make([]bool, N)
	d[0] = 0
	ans := 0
	for {
		cur := 0
		minCost := INF
		for i := 0; i < N; i++ {
			if !seen[i] && d[i] < minCost {
				minCost = d[i]
				cur = i
			}
		}
		if minCost == INF {
			break
		}
		seen[cur] = true
		ans += d[cur]
		for i := 0; i < N; i++ {
			cost := G[cur][i]
			if cost != -1 && cost < d[i] {
				d[i] = cost
			}
		}
	}

	fmt.Fprintln(wtr, ans)
	wtr.Flush()
}

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;
}

C++: #include <iostream>

using namespace std;

static const int N = 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[N][N];

int prim()
{
	int d[N], p[N], color[N];

	for (int i = 0; i < n; ++i)
	{
		d[i] = INFTY;
		p[i] = -1;
		color[i] = WHITE;
	}

	d[0] = 0;

	while (1)
	{
		int u = -1;
		int minv = INFTY;
		for (int i = 0; i < n; ++i)
		{
			if (minv > d[i] && color[i] != BLACK)
			{
				minv = d[i];
				u = i;
			}
		}

		if (u == -1) break;
		color[u] = BLACK;

		for (int v = 0; v < n; ++v)
		{
			if (m[u][v] != INFTY && color[v] != BLACK && m[u][v] < d[v])
			{
				d[v] = m[u][v];
				p[v] = u;
				color[v] = GRAY;
			}
		}
	}

	int s = 0;
	for (int i = 0; i < n; ++i)
	{
		if (p[i] != -1) s += m[p[i]][i];
	}

	return s;
}

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;
	return 0;
}

C++: #include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>

using namespace std;

// ---------------------
// repetition
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

// debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

// ---------------------
#define INF 922337203685477580
typedef long long ll;

int main() {
  int n;
  cin >> n;

  int G[n][n];
  int visited[n];
  int d[n];
  int p[n];
  REP(y, n) {
    REP(x, n) {
      int cost;
      cin >> cost;

      if (cost == -1) {
        G[y][x] = 1 << 15;
      } else {
        G[y][x] = cost;
      }
    }
    visited[y] = 0;
    d[y] = 1 << 15;
    p[y] = -1;
  }

  d[0] = 0;

  REP(_, n) {
    int mincost = 1 << 15;
    int minv = -1;
    REP(v, n) {
      if (!visited[v] && d[v] < mincost) {
        minv = v;
        mincost = d[v];
      }
    }
    visited[minv] = 1;
    REP(to, n) {
      if (!visited[to] && G[minv][to] < (1 << 15) && G[minv][to] < d[to]) {
        d[to] = G[minv][to];
        p[to] = minv;
      }
    }
  }

  ll sum = 0;
  REP(i, n) {
    if (p[i] != -1) {
      sum += G[i][p[i]];
    }
  }

  cout << sum << endl;
  return 0;
}