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>
#include <numeric>
#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define SORT_INV(c) sort((c).begin(), (c).end(), greater<int>())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG true
#define LL long long
#define Num 1000000007
// sort(a.begin(), a.end(), std::greater<int>());
using namespace std;
struct edge
{
    int to, cost;
};

typedef pair<int, int> P;
int main()
{
    int n;
    cin >> n;
    vector<edge> g[n];
    rep(i, n)
    {
        rep(j, n)
        {
            int temp = 0;
            edge ed;
            cin >> temp;
            if (temp == -1)
                ed.cost = INT_MAX;
            else
                ed.cost = temp;
            ed.to = j;
            g[i].push_back(ed);
        }
    }
    //solve by  fast prim
    bool used[n];
    int mincost[n];
    rep(i, n)
    {
        used[i] = false;
        mincost[i] = INT_MAX;
    }
    int ans = 0;
    mincost[0] = 0;
    priority_queue<P, vector<P>, greater<P>> que;
    que.push(P(0, 0));
    while (que.empty() == false)
    {
        auto p = que.top();
        que.pop();
        int v = p.second;
        if (mincost[v] < p.first || used[v] == true)
            continue;
        used[v] = true;
        ans += p.first;
        rep(i, g[v].size())
        {
            auto e = g[v][i];
            mincost[e.to] = min(mincost[e.to], e.cost);
            que.push(P(mincost[e.to], e.to));
        }
    }
    cout<<ans<<endl;
    return 0;
}

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

int root(int i,vector<int> &parent){
    if(parent[i]==-1){
        //親がいない時
        return i;
    }else{
        int result=root(parent[i],parent);
        parent[i]=result; //パス圧縮
        return result;
    }
}

void unite(int x,int y,vector<int> &parent){
    if(root(x,parent)!=root(y,parent)){
        parent[root(y,parent)]=root(x,parent);
    }
}

bool issame(int x,int y,vector<int> &parent){
    return root(x,parent)==root(y,parent);
}

int main(){
    int n;
    cin >> n;
    //first:cost,second:(first:from,second:to)
    vector<pair<int,pair<int,int> > > bridges(n*n);

    //入力
    for(int i=0;i<n;++i){
        for(int j=0;j<n;++j){
            int cost;
            if(cin >> cost,cost!=-1){
                bridges.push_back(pair<int,pair<int,int> >(cost,pair<int,int>(i,j)));
            }
        }
    }

    //sort
    sort(bridges.begin(),bridges.end());

    //島を管理する用
    vector<int> parents(n*n,-1);

    int sum=0;

    for(int i=0;i<bridges.size();++i){
        if(!issame(bridges[i].second.first,bridges[i].second.second,parents)){
            unite(bridges[i].second.first,bridges[i].second.second,parents);
            sum+=bridges[i].first;
        }
    }
    cout << sum;
}

C++: #include <algorithm>
#include <cstdint>

using namespace std;

enum status_t {
  WHITE,
  GRAY,
  BLACK,
};

#define GRAPH_SIZE 101

static uint32_t graph[GRAPH_SIZE][GRAPH_SIZE];
static status_t state[GRAPH_SIZE];
static uint32_t shortest_path[GRAPH_SIZE];

size_t minimum_spanning_tree(size_t num)
{
  size_t minimum_cost = 0;

  while (true) {
    uint32_t minimum = UINT32_MAX;
    uint32_t to = 0;
    for (uint32_t j = 0; j < num; j++) {
      if ((shortest_path[j] < minimum) && state[j] != BLACK) {
        minimum = shortest_path[j];
        to = j;
      }
    }

    if (minimum == UINT32_MAX) break;

    state[to] = BLACK;
    minimum_cost += minimum;

    for (uint32_t j = 0; j < num; j++) {
      if (state[j] != BLACK) {
        shortest_path[j] = min(shortest_path[j], graph[to][j]);
      }
    }
  }

  return minimum_cost;
}

#include <iostream>

int32_t main()
{
  uint32_t num;
  cin >> num;

  for (uint32_t i = 0; i < num; i++) {
    for (uint32_t j = 0; j < num; j++) {
      int32_t val;
      cin >> val;
      if (val == -1) {
        graph[i][j] = UINT32_MAX;
      } else {
        graph[i][j] = val;
      }
    }
  }

  cout << minimum_spanning_tree(num) << endl;

  return 0;
}