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 <iostream>
#include <queue>
#include <climits>
using namespace std;

const int N = 100;
int n;
int A[N][N];
bool visit[N] = {0};
priority_queue< pair<int, int> > Q;

int main()
{
	cin >> n;
	for (int i=0; i<n; i++)
	{
		for (int j=0; j<n; j++)
		{
			cin >> A[i][j];
		}
	}

	Q.push(pair<int, int>(0,0));
	visit[0] = true;

	int cost = 0;

	while (Q.size())
	{
		pair<int, int> q = Q.top();
		Q.pop();
		int k = q.second;
		if (visit[k]) continue;
		cost += q.first;
		visit[k]=true;
		for(int j=0;j<n;j++)
		{
			int c = A[k][j];
			if (c <= 0) continue;
			if (visit[j]) continue;
			Q.push(pair<int, int>(-c,j));
		}
	}

	cout << -cost << endl;
		
	return 0;
}

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;
    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(color[i] != BLACK && minv > d[i]){
                u = i;
                minv = d[i];
            }
        }

        if(u == -1) break;

        color[u] = BLACK;
        for(int v = 0; v < n; v++){
            if(M[u][v] != INF && color[v] != BLACK && d[v] > M[u][v]){
                d[v] = M[u][v];
                p[v] = u;
                color[v] = GRAY;
            }
        }
    }

    int sum = 0;

    for(int v = 0; v < n; v++){
        if(p[v] != -1)  sum += M[p[v]][v];
    }

    return sum;
}

int main(){
    cin >> n;

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

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

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;
}