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>
using namespace std;

int P[101];

void init(int N)
{
	for (int i=0; i<N; ++i) 
	    P[i] = i;
} 

int root(int a)
{
	if(P[a]==a)   
	   return a;
	else  return(P[a]=root(P[a]));
}
 
bool is_same_set(int a,int b)
{
	return(root(a)==root(b));
}

void unite(int a,int b)
{
	P[root(a)]=root(b);
}

int main()
{
	int n;
	cin >> n;
	init(n);
	int a[101][101];
	for(int i=0;i<n;i++)
	   for(int j=0;j<n;j++)
	       cin >> a[i][j];
	int M=0;
	int cost[10100],src[10100],dst[10100];
	for(int r=0;r<n;r++)
	   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++;
		  }
	pair<int,int> edges[10100];
	for(int i=0;i<M;i++)
	{
		edges[i].first=cost[i];
		edges[i].second=i;
	}
	sort(edges,edges+M);
	int sum=0;
	for(int i=0;i<M;i++)
	{
		if(is_same_set(src[edges[i].second],dst[edges[i].second]))
		  continue;
		unite(src[edges[i].second],dst[edges[i].second]);
		sum+=edges[i].first;
	}
	cout << sum << endl;
}

C++: #include <stdio.h>
#define MAX 100
#define INFTY 100000000
#define WHITE 0
#define BLACK 2
#define GRAY 1

int n, M[MAX][MAX];

int prim(){
    int u,minv;
    int d[MAX],p[MAX],color[MAX];
    
    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(){
    scanf("%d",&n);
    for(int i=0; i<n; i++){
        for(int j=0; j<n; j++){
            int e;
            scanf("%d",&e);
            M[i][j] = (e == -1) ? INFTY:e;
            
        }
    }
    printf("%d\n", prim());
    return 0;
}

C++: #if 0

#endif

#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

int P[10010];
void init(int N) {
  for (int i=1; i<=N; ++i)
    P[i] = i;
}
int root(int a) {
  if (P[a] == a)
    return a;
  return (P[a] = root(P[a]));
}
bool is_same_set(int a, int b) {
  return root(a) == root(b);
}
void unite(int a, int b) {
  P[root(a)] = root(b);
}

int n;

int main() {
  cin >> n;
  init(n);
  vector<pair<int,int>> NC;
  int src[10010]; int dst[10010];
  int ind = 0;
  int c;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> c;
      if (i < j && c >= 0) {
        ind++;
        NC.push_back(make_pair(c, ind));
        src[ind] = i; dst[ind] = j;
      }
    }
  }
  sort(NC.begin(), NC.end());
  int ans = 0;
  int cst, id, s, d;
  for (int i = 0; i < ind; i++) {
    cst = NC[i].first; id = NC[i].second;
    s = src[id]; d = dst[id];
    if (!(is_same_set(s, d))) {
      ans += cst;
      unite(s, d);
    }
  }
  cout << ans << endl;
}

C++: #include <iostream>
#include <cstdio>
#include <vector>
#include <queue>
#include <algorithm>
using namespace std;

#define MAX_N 100
#define MAX_EDGE_COST 20000
int Graph[MAX_N+1][MAX_N+1];
int n;

int prim(int initial_vertex) {
  bool visited[n+1];
  for(int i=1;i<=n;i++) visited[i] = false;
  vector<int> vertexes;
  vertexes.push_back(initial_vertex);
  visited[initial_vertex] = true;
  int total_edge_cost = 0;
  while(vertexes.size() < n) {
    // find minimum edge cost in vertexes
    int minimum_edge_cost = MAX_EDGE_COST;
    int next_v;
    for(int i=0;i<vertexes.size();i++) {
      int v = vertexes[i];
      for(int j=1;j<=n;j++) {
        if(!visited[j]) {
          if(Graph[v][j] != -1) {
            if(Graph[v][j] < minimum_edge_cost) {
              minimum_edge_cost = Graph[v][j];
              next_v = j;
            }
          }
        }
      }
    }
    visited[next_v] = true;
    vertexes.push_back(next_v);
    total_edge_cost += minimum_edge_cost;
  }
  return total_edge_cost;
}

int main() {
  scanf("%d",&n);
  for(int i=1;i<=n;i++) {
    for(int j=1;j<=n;j++) {
      scanf("%d ",&Graph[i][j]);
    }
  }
  printf("%d\n",prim(1));
}

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,min;
int d[MAX],p[MAX],color[MAX];

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

d[0]=0;

while(1){
min=INFTY;
u=-1;
for(int i=0;i<n;i++){
if(min>d[i]&&color[i]!=BLACK){
u=i;
min=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 <algorithm>
#include <string>
#include <stack>
#include <cstdlib>
#include <queue>
#include <vector>
#include <set>
#include <stdio.h>
#include <cstdio>
using namespace std;
int p[10001],s[10001],t[10001],cost[10001];
int root(int a) {
	if (p[a] == a) return a;
	return (p[a] = root(p[a]));
}
void unite(int a,int b){
	p[root(a)] = root(b);
}
bool same(int a ,int b){
	if (root(a) == root(b)) return 1;
	else return 0;
}
bool rcheck(int a){
	if (root(a) == a) return 1;
	else return 0;
}
pair <int,int> path[10001];
int main() {
	int n,coun = 0;
	cin >> n;
	for (int i = 0; i < n; i++){
		p[i] = i;
		for (int j = 0;j<n;j++) {
			s[n*i+j] = i; t[n*i+j]=j; 
			cin >> cost[n*i+j];
		}
	}
	for (int i = 0;i < n*n;i++) {
		path[i].first = cost[i];
		path[i].second = i;
	}
	sort(path,path+n*n);
	for (int i = 0; i < n*n;i++) {
		if (path[i].first > 0) {
			if(same(s[path[i].second],t[path[i].second]) == 0) {
				unite(s[path[i].second],t[path[i].second]);
				coun += path[i].first;
			}
		}
	}
	cout << coun << endl;
}