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>
#include <string>
#define MAX_N 110
using namespace std;
typedef long long ll;
const int INF = 1<<30; 
const int MOD = 1e9 + 7;
int cost[MAX_N][MAX_N], mincost[MAX_N];
bool used[MAX_N];
int prim(int n)
{
    int res = 0;
    mincost[0] = 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]);
    }
    return res;
}
int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n; cin >> n;
    for(int i = 0; i < MAX_N; i++) used[i] = false;
    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < n; j++)
        {
            cin >> cost[i][j];
            if(cost[i][j] == -1) cost[i][j] = INF;
        }
        mincost[i] = INF;
    }
    int ans = prim(n);
    cout << ans << 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;
  int d[MAX], p[MAX], color[MAX]; // d:??±??? ,p:??????v?????? ,color:????????????

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

  d[0] = 0;
  
  while(1){

    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>
using namespace std;

const int Max = 105;
const int INF = (1<<29);
int n, G[Max][Max], Min;
set<int> T;
set<int> V;

void Pime0(int u)
{
    T.insert(u);
    V.erase(u);
    set<int>::iterator i, j;
    while(T.size()<n)
    {
        int minv = INF;
        int index = -1;
        for(i=T.begin(); i!=T.end(); i++)
        {
            for(j=V.begin(); j!=V.end(); j++)
            {
                if(G[*i][*j]!=INF && minv>G[*i][*j])
                {
                    minv = G[*i][*j];
                    index = *j;
                }
            }
        }
        T.insert(index);
        V.erase(index);
        Min += minv;
    }
}
int main()
{
    cin >> n;
    Min = 0;
    for(int i=0; i<n; i++)
    {
        V.insert(i);
    }
    for(int i=0; i<n; i++)
    {
        for(int j=0; j<n; j++)
        {
            cin >> G[i][j];
            if(G[i][j]==-1)
                G[i][j] = INF;
        }
    }
    Pime0(0);
    cout << Min << endl;
    return 0;
}

C++: #include<iostream>
#include<utility>
#include<algorithm>
using namespace std;
int p[101];
void makeset(int N){
    for(int i=0;i<N;++i){
        p[i]=i;
    }
}
int root(int x){
    if(p[x]==x) return x;
    return (p[x]==root(p[x]));
}
void unite(int x,int y){
    p[root(x)]=root(y);
}
bool same(int x,int y){
    return root(x)==root(y);
}
int main(){
    int N,M=0;
    int A[101][101],cost[101],src[101],dst[101];
    cin>>N;
    makeset(N);
    for(int r=0;r<N;++r){
        for(int c=0;c<N;++c){
            cin>>A[r][c];
        }
        for(int c=r+1;c<N;++c){
            if(A[r][c]>-1){
                cost[M]=A[r][c];
                src[M]=r;
                dst[M]=c;
                M+=1;
            }
        }
    }
    pair<int,pair<int,int>>edges[101];
    for(int i=0;i<M;++i){
       edges[i]=make_pair(cost[i],make_pair(src[i],dst[i]));
    }
    sort(edges,edges+M);
    //for(int i=0;i<M;++i){
        //cout<<edges[i].first<<edges[i].second.first<<edges[i].second.second<<endl;
    //}
    int total=0,num=0,flag=0;
    for(int i=0;i<M;++i){
        //if(same(edges[i].second.first,edges[i].second.second)){continue;}
        //else{
            unite(edges[i].second.first,edges[i].second.second);
            total+=edges[i].first;
            num++;
            cout<<edges[i].first<<edges[i].second.first<<edges[i].second.second<<endl;
        //}
        if(num==N-1){
            flag=1;
            break;
        }
    }
    if(flag){
        cout<<total<<endl;
    }
}