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;
#define int long long

struct edge{ int to,cost; };
const int N = 1e5+10;
vector< edge > G[N];

int prim(){
  typedef pair<int, int> P;
  const int INF = 1 << 30;

  priority_queue<P,vector<P>,greater<P>> que;
  vector<bool> visited(N,false);

  que.push({0,0}); //{距離,頂点}
  int total = 0;

  while( !que.empty() ){
    P p = que.top(); que.pop();
    int v = p.second;
    if(visited[v]) continue;
    visited[v] = true;
    total += p.first;
    for(auto e : G[v]){
      if(!visited[e.to]){
        que.push( {e.cost,e.to} );
      }
    }
  }
  return total;
}

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int V; cin >> V;
  for(int i = 0; i < V; i++){
    for(int j = 0; j < V; j++){
      int cost; cin >> cost;
      if(cost == -1) continue;
      G[i].push_back({j,cost});
    }
  }
  cout << prim() << endl;

  return 0;
}

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

#define NUM 100
#define BLACK 0
#define GREY 1
#define WHITE 2
#define NIL -1
#define INF 1000000000
int A[NUM][NUM];

int V[NUM];
int color[NUM];

void init(){
    for(int i = 0; i < NUM; i++){
        color[i] = WHITE;
        V[i] = INF;
    }

}

int main(void){
    init();

    int n;
    scanf("%d", &n);

    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            scanf("%d", &A[i][j]);
        }
    }

    int next_node = 0;
    int sum = 0;
    while(1){
        color[next_node] = BLACK;
        for(int i = 0; i < n; i++){
            if(A[next_node][i] == NIL){
                continue;
            }
            V[i] = min(V[i], A[next_node][i]);
        }

        next_node = NIL;
        int min_dist = INF;
        for(int i = 0; i < n; i++){
            if(color[i] == BLACK){
                continue;
            }
            if(V[i] < min_dist){
                next_node = i;
                min_dist = V[i];
            }
        }
        if(min_dist == INF){
            break;
        }else{
            sum += min_dist;
        }
    }

    printf("%d\n", sum);
}

C++: #include<iostream>
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 u, minv;
	int d[MAX], p[MAX], color[MAX];

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

	d[0] = 0;

	while (true) {
		minv = INFTY;
		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&&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 (int i = 0; i < n; i++) {
		if (p[i] != -1)sum += M[i][p[i]];
	}

	return sum;	
}

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 <set>

#define rep(i, n) for (int i = 0; i < (int)(n); ++i)

const int INF = 1 << 21;
const int SIZE = 101;
int a[SIZE][SIZE];

int prim(int n) {
  int d[n], p[n], state[n];

  rep(i, n) {
    d[i] = INF;
    p[i] = -1;
    state[i] = 0;
  }

  d[0] = 0;

  while (1) {
    int minv = INF, u = -1;

    rep(i, n) {
      if (d[i] < minv && state[i] != 1) {
        minv = d[i];
        u = i;
      }
    }

    if (u == -1) break;
    state[u] = 1;

    rep(i, n) {
      if (a[u][i] != INF && state[i] != 1) {
        if (d[i] > a[u][i]) {
          d[i] = a[u][i];
          p[i] = u;
        }
      }
    }
  }

  int sum = 0;
  rep(i, n) {
    if (p[i] != -1) { sum += a[i][p[i]]; }
  }

  return sum;
}

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

  rep(i, n) rep(j, n) {
    int m;
    std::cin >> m;
    if (m == -1) m = INF;
    a[i][j] = m;
  }

  std::cout << prim(n) << '\n';

  return 0;
}