Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

type ElementKey int
type Node struct {
	key    ElementKey
	parent *Node
	rank   int
}

func newNode(key ElementKey) *Node {
	node := Node{}
	node.key = key
	node.parent = &node
	node.rank = 0

	return &node
}

func union(x, y *Node) {
	xSet := findSet(x)
	ySet := findSet(y)
	link(xSet, ySet)
}

func link(x, y *Node) {
	if x.rank > y.rank {
		y.parent = x
	} else {
		x.parent = y

		if x.rank == y.rank {
			y.rank++
		}
	}
}

func findSet(x *Node) *Node {
	if x != x.parent {
		x.parent = findSet(x.parent)
	}
	return x.parent
}

func newDisjointSets(nSets int) *DisjointSets {
	sets := DisjointSets{}
	sets.keyToNode = map[ElementKey]*Node{}
	for i := 0; i < nSets; i++ {
		key := ElementKey(i)
		sets.keyToNode[key] = newNode(key)
	}
	return &sets
}

type DisjointSets struct {
	keyToNode map[ElementKey]*Node
}

func (sets *DisjointSets) union(x, y ElementKey) {
	xNode := sets.keyToNode[x]
	yNode := sets.keyToNode[y]
	union(xNode, yNode)
}

func (sets DisjointSets) findSet(x ElementKey) *Node {
	xNode := sets.keyToNode[x]
	return findSet(xNode)
}

type Edge struct {
	i, j   int
	weight int
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	sets := newDisjointSets(n)
	edges := []Edge{}
	a := make([][]int, n)
	for i := 0; i < n; i++ {
		a[i] = make([]int, n)
		for j := 0; j < n; j++ {
			a[i][j] = nextInt()
			if a[i][j] >= 0 {
				e := Edge{
					i:      i,
					j:      j,
					weight: a[i][j],
				}
				edges = append(edges, e)
			}
		}
	}
	sort.Slice(edges, func(i, j int) bool { return edges[i].weight < edges[j].weight })
	totalWeight := 0
	for _, edge := range edges {
		i := ElementKey(edge.i)
		j := ElementKey(edge.j)
		if sets.findSet(i) != sets.findSet(j) {
			totalWeight += edge.weight
			sets.union(i, j)
		}
	}
	fmt.Println(totalWeight)
}

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

int n;
int a[101][101];
int flg[101];
int t[101];
int sum = 0;

void visit(){
  int ima = 0;
  int mine = 100000000;
  
  
  for(int k=0;k<n;k++) {
    
    for(int i=0;i<n;i++) {
      if(flg[i] == 0 && mine > t[i]) {
	mine = t[i];
	ima = i;
      }
    }
    sum += mine;
    flg[ima] = 1;
    
    for(int i=0;i<n;i++) 
      if(a[ima][i] != -1) 
	if(t[i] > a[ima][i] ) t[i] = a[ima][i];
    
    
  }
}

int main() {

  cin >> n;

  for(int i=0;i<n;i++) 
    for(int j=0;j<n;j++) 
      cin >> a[i][j];
  
  for(int i=0;i<n;i++) {
    flg[i] = 0;
      t[i] = 100000000;
  }
  
  t[0] = 0;
  flg[0] = 1;
  for(int i=0;i<n;i++) 
    if(a[0][i] != -1) t[i] = a[0][i];

  visit();

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

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,i,v;
    int d[MAX],p[MAX],color[MAX];
    int sum = 0;

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

    d[0] = 0;

    while(1)
    {
        minv = INFTY;
        u = -1;

        for(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(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;
                }
            }
        }
    }

   

    for(i=0;i<n;i++)
    {
        if(p[i] != -1) sum += M[i][p[i]];
    }

    return sum;
}

int main()
{
    int i,j,e;
    cin >> n;

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

    cout << prim() << endl;

    return 0;
    
}

C++: #include <bits/stdc++.h>
#define rep(i, a, b) for(int i = a; i < b; i++)
#define Rep(i, a, b) for(int i = a; i <= b; i++)
#define _GLIBCXX_DEBUG
#define Vl vector<ll>
#define Vs vector<string>
#define Vp vector<pair<ll, ll>>
#define ll long long
#define ALL(v) (v).begin(),(v).end()
using namespace std;
const double pi = acos(-1.0);
const ll MOD = 1e9 + 7;
const ll INF = 1LL << 60;
using Graph = vector<vector<ll>>;

ll n;
ll M[110][110]; // kyori
const int white = 0, gray = 1, black = 2;

ll prim(){
  ll u, minv;
  ll d[10000], p[10000], color[10000];

  rep(i, 0, n){
    d[i] = INF;
    p[i] = -1; // parent
    color[i] = white;
  }
  d[0] = 0;
  while(1){
    minv = INF;
    u = -1;
    rep(i, 0, n){
      if(minv > d[i] && color[i] != black){
        u = i;
        minv = d[i];
      }
    }
    if(u == -1) break;
    color[u] = black;
    rep(v, 0, n){
      if(color[v] != black && M[u][v] != INF){
        if(d[v] > M[u][v]){
          d[v] = M[u][v];
          p[v] = u;
          color[v] = gray;
        }
      }
    }
  }
    ll sum = 0;
    rep(i, 0, n){
    if(p[i] != -1) sum += M[i][p[i]];
    }

    return sum;
}

int main() {
  cin >> n;
  rep(i, 0, n){
    rep(j, 0, n){
      ll a; cin >> a;
      M[i][j] = (a == -1) ? INF : a;
    }
  }

  cout << prim() << endl;

  return 0;
}

C++: // ALDS1_12_A: Minimum Spanning Sort
#include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
bool debug = false;
const int INF = 100000;
// const int BK = 0, GR = 1, WT = 2;

std::vector<std::vector<int>> adjacency_list;
std::vector<int> node_stats;
std::vector<std::pair<int, int>> weight_memo;

int PrimAlgorithm(int weight, int vertex) {
    node_stats.at(vertex) = 1;
    
    for (int i=0; i<adjacency_list.at(vertex).size(); i++) {
        int tmp_vertex = i;
        if (adjacency_list.at(vertex).at(tmp_vertex) != -1) {
            std::pair<int,int> tmp = std::make_pair(tmp_vertex, adjacency_list.at(vertex).at(tmp_vertex));
            weight_memo.push_back(tmp);
        }
    }
    
    int minimum_weight = INF, next_vertex = -1;
    for (int i=0; i<weight_memo.size(); i++) {
        int tmp_vertex = weight_memo.at(i).first, tmp_weight = weight_memo.at(i).second + weight;
        if (tmp_weight < minimum_weight) {    
            if (node_stats.at(tmp_vertex) == 0) {
                next_vertex = tmp_vertex;
                minimum_weight = tmp_weight;
            }
        }
    }
    if (debug) std::cout << "next_vertex = " << next_vertex << ", minimum_weight = " << minimum_weight << "\n";
    if (next_vertex == -1) {
        return weight;
    }
    return PrimAlgorithm(minimum_weight, next_vertex);
}

int main() {
    int total_num; std::cin >> total_num;
    adjacency_list.resize(total_num);
    for (int i=0; i<adjacency_list.size(); i++) adjacency_list.at(i).resize(total_num);
    for (int i=0; i<total_num; i++) {
        for(int j=0; j<total_num; j++) {
            std::cin >> adjacency_list.at(i).at(j);
        }
    }

    node_stats.resize(total_num);
    for (int i=0; i<node_stats.size(); i++) node_stats.at(i) = 0;

    int result = PrimAlgorithm(0, 0);
    std::cout << result << "\n";
}