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 "bits/stdc++.h"
using namespace std;
int main()
{
    int n, inf = 10000000;
    scanf("%d", &n);
    vector<vector<int>> a(n, vector<int>(n));
    for (int i = 0; i < n; i++)
    {
        for (int j = 0, k; j < n; j++)
        {
            scanf("%d", &k);
            a[i][j] = k == -1 ? inf : k;
        }
    }
    
    vector<int> cost(n, inf);
    vector<bool> vis(n, false);
    cost[0] = 0;
    for (int mi = inf, u = 0; ; mi = inf)
    {
        for (int i = 0; i < n; i++)
        {
            if (!vis[i])
            {
                if (cost[i] < mi)
                {
                    mi = cost[i];
                    u = i;
                }
            }
        }
        if (mi == inf)
        {
            break;
        }
        vis[u] = true;
        for (int i = 0; i < n; i++)
        {
            if (!vis[i] && a[u][i] != -1)
            {
                cost[i] = min(cost[i], a[u][i]);
            }
        }
    }
    printf("%d\n", accumulate(cost.begin(), cost.end(), 0));
}

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

class Edge {
public:
	int v1, v2, d;
};

int n, k=0, V[100];
Edge E[5000];

void Sort() {
	for (int i = 1; i < k; i++) {
		Edge v = E[i];
		int j = i - 1;
		while (j >= 0 && E[j].d > v.d) {
			E[j + 1] = E[j];
			j--;
		}
		E[j + 1] = v;
	}
}

int Kruskal() {
	int m = 0;
	for (int i = 0; i < k; i++) {
		Edge e = E[i];
		if (V[e.v1] != V[e.v2]) {
			int v = V[e.v1], u = V[e.v2]; m += e.d;
			for (int j = 0; j < n; j++) {
				if (V[j] == u) V[j] = v;
			}
		}
	}
	return m;
}

int main() {
	int g;
	cin >> n;
	for (int i = 0; i < n; i++) {
		V[i] = i;
		for (int j = 0; j < n; j++) {
			cin >> g;
			if (i < j && g > -1) {
				E[k].v1 = i; E[k].v2 = j; E[k].d = g; k++;
			}
		}
	}

	Sort();

	cout << Kruskal() << endl;
}