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>
using namespace std;

const int INF = 1 << 20;
const int MAX_N = 110;

int main() {
  int cost[MAX_N][MAX_N];
  int mincost[MAX_N];
  bool used[MAX_N];
  int n, a, res;

  cin >> n;

  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      cin >> a;
      cost[i][j] = a == -1 ? INF : a;
    }
  }

  for (int i = 0; i < n; ++i) {
    mincost[i] = INF;
    used[i] = false;
  }

  mincost[0] = 0;
  res = 0;

  while (true) {
    int v = -1;
    for (int u = 0; u < n; ++u) {
      if (!used[u] && (v == -1 || mincost[u] < mincost[v])) v = u;
    }

    if (v == -1) break;

    used[v] = true;
    res += mincost[v];

    for (int u = 0; u < n; ++u) {
      mincost[u] = min(mincost[u], cost[v][u]);
    }
  }

  cout << res << endl;
  
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <numeric>
#include <limits>

using namespace std;

const int N = 100;

enum {
    WHITE,
    GRAY,
    BLACK,
};

int main() {
    int A[N][N];

    int n;
    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            int a;
            cin >> a;
            A[i][j] = a == -1 ? numeric_limits<int>::max() : a;
        }
    }

    // ????????????
    vector<int> color(n, WHITE); // ??????????¨??????¶???
    vector<int> d(n, numeric_limits<int>::max());
    vector<int> p(n, -1);

    d[0] = 0;
    while (1) {
        int minv = numeric_limits<int>::max();
        int u = -1;
        for (int i = 0; i < n; ++i) {
            if (minv > d[i] && color[i] != BLACK) {
                u = i;
                minv = d[i];
            }
        }
        if (u == -1)
            break;
        color[u] = BLACK;
        for (int v = 0; v < n; ++v) {
            if (color[v] != BLACK && A[u][v] != numeric_limits<int>::max()) {
                if (d[v] > A[u][v]) {
                    d[v] = A[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }
    int sum;
    for (int i = 0; i < n; ++i) {
        if (p[i] != -1)
            sum += A[i][p[i]];
    }
    cout << sum << endl;

    return 0;
}

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

const long MAX = 100;
const long INFTY = (1<<21);
const long WHITE = 0;
const long GRAY = 1;
const long BLACK = 2;

long n, M[MAX][MAX];

long prim(){
	long u, minv;
	long d[MAX], p[MAX], color[MAX];

	// d: minimum dist. p: parent

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

	d[0] = 0;

	while (1){
		minv = INFTY;
		// u: node which has minv
		u = -1;
		for (long i = 0; i < n; i++){
			if (minv > d[i] && color[i] != BLACK){
				u = i;
				minv = d[i];
			}
		}
		// cut all nodes
		if (u == -1) break;
		color[u] = BLACK; // already selected
		for (long v = 0; v < n; v++){
			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;
	for (long i = 0; i < n; i++){
		if (p[i] != -1) sum += M[i][p[i]];
	}

	return sum;
}

int main(){
	cin >> n;

	for (long i = 0; i < n; i++){
		for (long j = 0; j < n; j++){
			long e;
			cin >> e;
			//M[i][j] = (e == -1) ? INFTY : e;
			if (e == -1) M[i][j] = INFTY;
			else M[i][j] = e;
		}
	}

	cout << prim() << endl;
}

C++: #include <stdio.h>
#include <stdlib.h>
#define MAX 101
#define rep(i,n) for(int i=0;i<n;i++)
#define infinity 1e9
typedef struct tuple{
    int a;
    int b;
    int w;
}tuple;
int n,t=0,cost=0;
int G[MAX][MAX],tags[MAX];
tuple v[5010];
int cmpAscW(const void * n1, const void * n2){
    if (((tuple *)n1)->w > ((tuple *)n2)->w)return 1;
	else if (((tuple *)n1)->w < ((tuple *)n2)->w)return -1;
	else return 0;
}
int min(int x,int y){
    if(x < y)return x;
    else return y;
}
int max(int x,int y){
    if(x<y)return y;
    else return x;
}
void Kruskal(){
    int m,temp=0;
    rep(i,t){
        if(tags[v[i].a] != tags[v[i].b]){
            temp = max(tags[v[i].a],tags[v[i].b]);
            m = min(tags[v[i].a],tags[v[i].b]);
            tags[v[i].a] = m;
            tags[v[i].b] = m;
            cost += v[i].w;
            for(int j=m;j<n;j++){
                if(tags[j] == temp)tags[j]=m;
            }
        }
    }
}
int main(){
    scanf("%d",&n);
    rep(i,5010){
        v[i].w = infinity;
    }
    rep(i,n){
        tags[i] = i;
        rep(j,n){
            scanf("%d",&G[i][j]);
            if(i<j){
                if(G[i][j] != -1){
                    v[t].a = i;
                    v[t].b = j;
                    v[t].w = G[i][j];
                    t++;
                }
            }
        }
    }
    qsort(v, t, sizeof(tuple), cmpAscW);
    Kruskal();
    printf("%d\n",cost);
    return 0;
}