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 <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;
}

C++: #include<bits/stdc++.h>
using namespace std;
const int MAX=101;
const int INF=123456789;


class union_find{
public:
  vector<int> rank,pare;
  union_find(){}
  union_find(int size){
    rank.resize(size,0);
    pare.resize(size,0);
    for(int i=0;i<size;i++){
      init(i);
    }
  }

  void init(int x){
    pare[x]=x;
    rank[x]=0;
  }

  int findpare(int x){
    if(pare[x]==x){
      return x;
    }
    else{
      return pare[x]=findpare(pare[x]);
    }
  }

  bool issame(int x,int y){
    return findpare(x)==findpare(y);
  }

  void unite(int x,int y){
    x=findpare(x);
    y=findpare(y);

    if(x==y) return;
    if(rank[x]<rank[y]){
      pare[x]=y;
    }
    else{
      pare[y]=x;
      if(rank[x]==rank[y]) rank[x]++;
    }
  }


};

int n,E;
struct edge{
  int u,v,cost;
};

edge es[MAX];


bool comp(const edge& e1,const edge& e2){
  return e1.cost<e2.cost;
}


int kruskal(){
  sort(es,es+E,comp);//E???????????°
  int res=0;
  union_find uf=union_find(n);
  for(int i=0;i<E;i++){
    edge e=es[i];
    if(!uf.issame(e.u,e.v)){
      uf.unite(e.u,e.v);
      res+=e.cost;
    }
  }
  return res;
}

int main(){
  cin>>n>>E;
  for(int i=0;i<E;i++){
    int s,t,w;
    cin>>s>>t>>w;
    es[i].u=s;
    es[i].v=t;
    es[i].cost=w;
  }

  cout<<kruskal()<<endl;
  return 0;
}