Go: package main

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

const (
	WHITE int = iota
	GRAY
	BLACK
)

type graph struct {
	G [][]int
	C []int
	D []int
	P []int
}

var INFTY = 1 << 32

func constructGraph() *graph {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	g := make([][]int, n)
	c := make([]int, n)
	d := make([]int, n)
	p := make([]int, n)

	for i := 0; i < n; i++ {
		sc.Scan()
		fields := strings.Fields(sc.Text())
		g[i] = toIntSlice(fields)
	}

	return &graph{g, c, d, p}
}

func (g *graph) initMst() {
	for i := 0; i < len(g.G); i++ {
		g.C[i] = WHITE
		g.D[i] = INFTY
	}
	g.D[0] = 0
	g.P[0] = -1
}

func (g *graph) primMst() int {
	g.initMst()

	var u int
	for {
		mincost := INFTY
		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.D[i] < mincost {
				mincost = g.D[i]
				u = i
			}
		}

		if mincost == INFTY {
			break
		}

		g.C[u] = BLACK

		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.existEdge(u, i) {
				if g.G[u][i] < g.D[i] {
					g.D[i] = g.G[u][i]
					g.P[i] = u
				}
			}
		}
	}

	totalCost := 0
	for _, cost := range g.D {
		totalCost += cost
	}
	return totalCost
}

func (g *graph) existEdge(u, v int) bool {
	return g.G[u][v] != INFTY && g.G[v][u] != INFTY
}

func toIntSlice(s []string) []int {
	a := make([]int, len(s))
	for i, v := range s {
		num, _ := strconv.Atoi(v)
		if num == -1 {
			num = INFTY
		}
		a[i] = num
	}
	return a
}

func main() {
	g := constructGraph()
	fmt.Println(g.primMst())
}

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;
}

C++: import java.util.ArrayList;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Scanner;

@SuppressWarnings("unchecked")
class MinCostTree{

    int N;
    class Edge{
        int from,to;
        long w;
        Edge(int from,int to,long w){this.from=from;this.to=to;this.w=w;}
    }
    List<Edge> edges[];
    List<Edge> minedge[];
    void add_edge(int u,int v,long w){
        edges[u].add(new Edge(u,v,w));
        edges[v].add(new Edge(v,u,w));
    }
    MinCostTree(int N){
        this.N=N;
        edges = new ArrayList[N];
        minedge = new ArrayList[N];
        for(int i=0;i<N;++i)edges[i]=new ArrayList<>();
        for(int i=0;i<N;++i)minedge[i]=new ArrayList<>();
    }
    long mincost(){
        PriorityQueue<Edge> que = new PriorityQueue<>((a,b)->a.w<b.w ? -1:1);
        boolean used[] = new boolean[N];
        used[0]=true;
        long res = 0;
        for(Edge e : edges[0])que.add(e);
        while(!que.isEmpty()){
            Edge e = que.poll();
            if(used[e.to])continue;
            used[e.to]=true;
            minedge[e.from].add(e);
            res += e.w;
            for(Edge ed : edges[e.to])que.add(ed);
        }
        return res;
    }
}

class Main{
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        MinCostTree mct = new MinCostTree(n);
        for(int i=0;i<n;++i){
            for(int j=0;j<n;++j){
                long a = scan.nextLong();
                if(i>j && a>0)mct.add_edge(i, j, a);
            }
        }
        System.out.println(mct.mincost());
    }
}

C++: #include <iostream>
using namespace std;
#define INF 1<<21
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define MAX 100

int v_num;
int adjM[MAX+1][MAX+1];

int PrimsAlgorithm() 
{
    int current_vertex;
    int color[v_num+1], min_edge[v_num+1], parent[v_num+1];

    // set init state
    for (int i = 0; i < v_num; ++i)
    {
        color[i] = WHITE;
        min_edge[i] = INF;
        parent[i] = -1;
    }

    min_edge[0] = 0;

    while (true) 
    {
        int min_cost = INF;
        // move to the minimum vertex which can be accessed 
        for (int i = 0; i < v_num; ++i) 
        {
            if (color[i] != BLACK && min_edge[i] < min_cost)
            {
                min_cost = min_edge[i];
                current_vertex = i;
            }
        }

        if (min_cost == INF) break;

        color[current_vertex] = BLACK;

        for (int i = 0; i < v_num; ++i) 
        {
            if (color[i] != BLACK && adjM[current_vertex][i] != -1)
            {
                if (adjM[current_vertex][i] < min_edge[i])
                {
                    min_edge[i] = adjM[current_vertex][i];
                    parent[i] = current_vertex;
                    color[i] = GRAY;
                }
            } 
        }
    }

    int sum = 0;
    for (int i = 0; i < v_num; ++i) 
    {
        if (parent[i] != -1) sum += adjM[i][parent[i]];
    }
    return sum;
}

int main() 
{
    int v;
    cin >> v_num;
    for (int i = 0; i < v_num; ++i) 
    {
        for (int j = 0; j < v_num; ++j)
        {
            cin >> v;
            adjM[i][j] = v != -1 ? v : INF;
        }
    }
    
    cout << PrimsAlgorithm() << endl;
}

C++: #include <iostream>

using namespace std;


class Graph{
private:

  int size;
  int **graph;
  int *state;

public:

  Graph(int size){
    int i;
    int j;
    this->size = size;
    this->state = new int[size];
    this->graph = new int*[size];
    for(i = 0;i < size;i++){
      this->graph[i] = new int[size];
    }
    for(i = 0;i < this->size;i++){
	this->state[i] = 0;
      }
  }

  ~Graph(){
    int i;
    for(i = 0;i < this->size;i++){
      delete[] this->graph[i];
    }
    delete[] this->graph;
  }

  int getMinimum(){
    int i;
    int j;
    int min;
    int res = 0;

    for(i = 0;i < this->size;i++){
      min = 0;

      for(j = 1;j < this->size;j++){
	if(this->graph[i][j] != -1 && this->state[j] == 0){
	  if(this->graph[i][j] <= this->graph[i][min] 
	     ||	this->graph[i][min] == -1){
	    min = j;
	  }
	}
      }

      if(state[min] == 0){
	state[min] = 1;
	res += graph[i][min];
      }
    }
    return res;
  }

  void setValue(int x,int y,int value){
    this->graph[x][y] = value;
  }

};

int main(){

  int i;
  int j;
  int n;
  int a;

  Graph *graph;

  cin >> n;

  graph = new Graph(n);

  for(i = 0;i < n;i++){
    for(j = 0;j < n;j++){
      cin >> a;
      graph->setValue(i,j,a);
    }
  }

  cout << graph->getMinimum() << endl;

  delete graph;

  return 0;
}