Go: package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

C++: #include<iostream>
#include<algorithm>
#define INF 99999
using namespace std;

int G[110][110] = {};

int prim(int n)
{
    int mini[110];
    int used[110];

    //init
    for(int i = 0;i < n;i++){
        mini[i] = INF;
        used[i] = 0;
    }
    mini[0] = 0;
    int ans = 0;

    while(true)
    {
        int v = -1;
        for(int i = 0;i < n;i++){
            if(!used[i] && (v == -1 || mini[i] < mini[v])) v = i;
        }
        if(v == -1) break;
        //ans = -1;

        used[v] = 1;
        ans += mini[v];
        //cout << ans << endl;

        for(int i = 0;i < n;i++){
            mini[i] = min(mini[i], G[v][i]);
        }
    }
    return ans;
}

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

    for(int i = 0;i < n;i++){
        for(int j = 0;j < n;j++){
            int cost;
            cin >> cost;
            if(cost == -1) G[i][j] = INF;
            else G[i][j] = cost;
        }
    }

    cout << prim(n) << endl;
    return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef vector<vector<int> > vvi;
typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<string, int> psi;
typedef pair<int, int> pii;
#define rep(i,s,n) for(int i = (s); i < (n); i++)
#define loop(i) for(int i = 0;true; i++)
#define all(x) (x).begin(), (x).end()
#define yn(f) (f?"yes":"no")
#define YN(f) (f?"YES":"NO")
#define Yn(f) (f?"Yes":"No")
#define mn 1000000007
#define INT32_MAX 2147483647

int main() {
	int N;
	cin >> N;
	vvi A(N,vi(N));
	for (int i = 0; i < N; i++)
	{
		for (int j = 0; j < N; j++)
		{
			cin >> A[i][j];
			if (A[i][j] == -1)A[i][j] = INT32_MAX;
		}
	}
	vi used(N, 0);
	vi mincost(N,INT32_MAX);
	int total = 0;
	mincost[0] = 0;
	while (true) {
		int minIndex = -1;
		for (int u = 0; u < N; u++) {
			if (used[u]==0 && (minIndex == -1 || mincost[u] < mincost[minIndex])) minIndex = u;
		}
		if (minIndex == -1) break;
		used[minIndex] = 1;
		total += mincost[minIndex];
		for (int u = 0; u < N; u++)
		{
			mincost[u] = min(mincost[u], A[minIndex][u]);
		}
	}
	cout << total << endl;
};

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-1;k++) {
    mine = 10000000;
    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>
#include<string>
using namespace std;

int prim();
int Infty = 20000000;

int n,*d,*p,**G;
string *color;

int main(){
	cin>>n;
	d = new int[n]; p = new int[n];
	d = d-1; p = p-1;
	G = new int*[n]; for(int i=0;i<n;i++) G[i] = new int[n];
	G = G-1; for(int i=1;i<=n;i++) G[i] = G[i]-1;
	color = new string[n]; color = color-1;

	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++) cin>>G[i][j];
	}

	cout<<prim()<<endl;

	delete [] (d+1); delete [] (p+1);
	for(int i=1;i<=n;i++) delete [] (G[i]+1); delete [] (G+1);
	delete [] (color+1);
}

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

	while(1){
		int u , mincost = Infty;
		for(int i=1;i<=n;i++){
			if(color[i]!="BLACK"&&d[i]<mincost){
				mincost = d[i];
				u = i;
			}
		}

		if(mincost==Infty) break;

		color[u] = "BLACK";

		for(int v=1;v<=n;v++){
			if(color[v]!="BLACK" && G[u][v]!=-1){
				if(G[u][v]<d[v]){
					d[v] = G[u][v];
					p[v] = u;
					color[v] = "GRAY";
				}
			}
		}
	}

	int sum = 0;
	for(int i=1;i<=n;i++){
		sum += d[i];
	}
	return sum;
}

C++: #include <iostream>
using namespace std;
static const int MAX = 100;
static const int INF = (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;
  // d: TとT-Vをつなぐ重みが最小の辺の重み
  // p: p[v]に頂点vの親
  int d[MAX], p[MAX], color[MAX];

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

  d[0] = 0;

  while (1) {
    minv = INF;
    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] != INF) {
        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) ? INF : e;
    }
  }

  cout << prim() << endl;
}

C++: #include <iostream>
using namespace std;
#define N 100
#define INF 9999999
int M[N][N];
int mincost[N];
bool used[N];
int n;
int prim(){
  for(int i=0;i<n;i++){
    used[i]=false;
    mincost[i]=INF;
  }
  mincost[0]=0;
  int res=0;

  while(true){
    int v=-1;
    for(int i=0;i<n;i++){
      if(!used[i] && (v==-1||mincost[i]<mincost[v])){
        v=i;
      }
    }
    if(v==-1) break;
    used[v]=true;
    res+=mincost[v];

    for(int i=0;i<n;i++){
      mincost[i]=min(mincost[i], M[v][i]);
    }
  }
  return res;
}
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)?INF:e;
    }
  }
  cout<<prim()<<"\n";

}