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;
#define MAX 100
#define INF 1 << 30
int n, A[MAX + 1][MAX + 1], d[MAX + 1];
bool vis[MAX + 1];

int prim(int s){
  int sum = 0;
  for ( int i = 1; i <= n; i++){
    d[i] = A[s][i];
    vis[i] = false;
  }
  d[s] = 0;
  vis[s] = true;

  while ( 1 ){
    int minCost = INF;
    for ( int i = 1; i<=n; i++){
      if ( minCost > d[i] && !vis[i]){
        minCost = d[i];
        s = i;
      }
    }

    if ( minCost == INF)break;

    sum += minCost;
    vis[s] = true;

    for ( int i = 1; i <= n; i++){
      if ( d[i] > A[s][i] && !vis[i]){
        d[i] = A[s][i];
      }
    }
  }

  return sum;
}

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

  cout << prim(1) << endl;

  return 0;
}

C++: #include <cstdio>
#include <vector>

int main(void){
	int n, min_edge, next_node, count, sum;
	scanf("%d", &n);
	std::vector<std::vector<int>> edges;
	std::vector<int> isUsed;
	edges.resize(n);
	isUsed.resize(n);
	for(int i=0;i<n;i++){
		isUsed[i]=-1;
		edges[i].resize(n);
		for(int j=0;j<n;j++){
			scanf("%d", &edges[i][j]);
		}
	}

	min_edge=3000;
	isUsed[0] = 1;
	count = 0;
	sum=0;
	while(count<4){
		for(int i=0;i<n;i++){
			if(isUsed[i]==1){
				for(int j=0;j<n;j++){
					if (isUsed[j]==-1 && edges[i][j]>-1 && edges[i][j]<min_edge){
						min_edge = edges[i][j];
						next_node = j;
					}
				}
			}
		}
		sum += min_edge;
		isUsed[next_node]=1;
		min_edge = 3000;
		count += 1;
	}
	printf("%d\n", sum);
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#define PII pair<int,int>
#define MPII(a,b) make_pair(a,b)
using namespace std;
class NODE
{
public:
	vector<PII> v;
	int index = 0;
};
class Tree
{
public:
	vector<int> V;
	int cost = 0;
};

int main()
{
	NODE* nodes;
	nodes = new NODE[101];
	Tree T;
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		for (int j = 1; j <= n; j++)
		{
			int t;
			cin >> t;
			if (t != -1)
			{
				PII p = MPII(t, j);
				nodes[i].v.push_back(p);
			}
		}
		sort(nodes[i].v.begin(), nodes[i].v.end());
	}
	T.V.push_back(1);
	while (1)
	{
		if (T.V.size() == n+1)break;
		int mincost=INT_MAX;
		int addv=-1;
		int index;
		for (auto itr : T.V)
		{
			if (mincost >= nodes[itr].v[nodes[itr].index].first)
			{
				mincost = nodes[itr].v[nodes[itr].index].first;
				addv = nodes[itr].v[nodes[itr].index].second;
				index = itr;
			}
		}
		nodes[index].index++;
		T.V.push_back(addv);
		T.cost += mincost;
	}
	cout << T.cost << endl;
	delete[] nodes;
	return 0;
}

C++: #include <iostream>
#define N 100
#define INFINITY 2000000000
using namespace std;
void prim();
int M[N][N],d[N],p[N],u,n,mincost,i,j;
string color[N];
int main(){
  cin >> n;
  for(i=0;i<n;i++){
    for(j=0;j<n;j++){
      cin >> M[i][j];
    }
  }
  prim();
  return 0;
}
void prim(){
  for(i=0;i<n;i++) color[i]="WHITE",d[i]=INFINITY;
  d[0]=0;
  p[0]=-1;
  while(1){
    mincost=INFINITY;
    for(i=0;i<n;i++){
      if(color[i]!="BLACK"&&d[i]<mincost){
	mincost=d[i];
	u=i;
      }
    }
    if(mincost==INFINITY) break;
    color[u]="BLACK";
    for(i=0;i<n;i++){
      if(color[i]!="BLACK"&&M[u][i]!=-1){
	if(M[u][i]<d[i]){
	  d[i]=M[u][i];
	  p[i]=u;
	  color[i]="GLAY";
	}
      }
    }
  }
  int sum=0;
  for(i=0;i<n;i++) sum+=d[i];
  cout << sum << endl;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#define INF 1e9
using namespace std;

int main(){
    //declaration and input
    int n;
    cin >> n;
    vector<vector<int>> graph(n, vector<int>(n));
    for (int i = 0; i < n; i++) for (int j = 0; j < n; j++) cin >> graph[i][j];
    
    //get Minimum Spanning Tree by Prim's algorithm
    vector<int> parent_of(n, -1);
    vector<int> cost(n, INF);
    vector<int> state(n, 0);
    cost[0] = 0;
    state[0]++;

    int sum = 0;
    int parent = -1;
    while (true){
        int min_cost = INF;
        int next = -1;
        for (int i = 0; i < n; i++){
            if (state[i] == 1 && cost[i] < min_cost){
                min_cost = cost[i];
                next = i;
            }
        }
        if (min_cost == INF)
            break;
        sum += cost[next];
        state[next] = 2;
        for (int i = 0; i < n; i++){
            if (state[i] != 2 && graph[i][next] != -1){
                state[i] = 1;
                if (cost[i] > graph[i][next])
                    cost[i] = graph[i][next];
            }
        }
    }

    /*int sum = 0;
    for (int i = 0; i < n; i++){
        if (parent_of[i] != -1)
            sum += graph[i][parent_of[i]];
    }*/

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