Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

C++: #include <iostream>
using namespace std;
#define INF 1000000

int main(){
  long n;
  long G[100][100],d[100];
  long minc,mi,i;
  bool flg[i];
  long sum=0;
  
  cin >> n;
  for (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;
    }
    d[i]=INF;
    flg[i]=false;
  }

  d[0]=0;
  while (true){
    minc=INF;
    for (i=0;i<n;i++){
      if (!flg[i]&&d[i]<minc){
	minc=d[i];
	mi=i;
      }
    }
    if (minc==INF) break;
    flg[mi]=true;
    for (i=0;i<n;i++){
      if (G[mi][i]==INF)continue;
      if (!flg[i]&&d[i]>G[mi][i]){
	d[i]=G[mi][i];
	//cout << d[i];
      }
    }
  }
  
  for (i=0;i<n;i++){
    sum+=d[i];
  }
  cout << sum<<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 (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() {


	int s;

	cin >> n;

	for (int i = 0;i < n;i++) {
		for (int k = 0; k < n; k++)
		{
			cin >> s;
			m[i][k] = (s == -1) ? inf : s;
		}
	}


	cout << prim() << endl;

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define INF 10000000

int prim(int v, vector<vector<pair<int, int> > > adjlist){

    priority_queue<pair<int, int> >  wait;    // first := 候補辺のコスト   second　:= 行先ノード
    vector<int> result(v, INF);               // 頂点iと木の間の最小コスト
    int ans = 0, size = 0;                    // 木のコスト　頂点数

    //初期条件
    result[0] = 0;
    wait.push(make_pair(0, 0));

    while(!wait.empty() && size < v){

        //候補辺のうち最小のものを取り出す
        int newpoint = wait.top().second;
        int newcost = -wait.top().first;
        wait.pop();

        if(result[newpoint] < newcost) continue;

        //出てきた頂点を木に追加
        ans += newcost;
        result[newpoint] = -INF;
        size++;

        // 新しい点から出ている辺をすべてなめる
        for(int i = 0; i < adjlist[newpoint].size(); i++){
            int nextpoint = adjlist[newpoint][i].second;
            int nextcost = adjlist[newpoint][i].first;
            //より木に近くなった頂点があれば,　そこへの枝をqueueに追加
            if(result[nextpoint] > nextcost){
                result[nextpoint] = nextcost;
                wait.push(make_pair(-nextcost, nextpoint));
            }
        }
    }

    return ans;
}


int main(){

    int V; cin >> V;     // V:= 頂点の数
    vector<vector<pair<int, int> > > adjlist(V);      //first := コスト　second := 行先

    //入力
    for(int i = 0; i < V; i++){
        for(int j = 0; j < V; j++){
            int a; cin >> a;
            if(a == -1) continue;
            else{
                adjlist[i].push_back(make_pair(a, j));
            }
        }  
    }

    int ans = prim(V, adjlist);

    cout << ans << endl;
    return 0;
}

C++: #include "stdafx.h"
#include <iostream>

#define MAX 100000000;
using namespace std;

int main(void)
{
	int n, now = 0, flag[101] = {};
	long ans = 0, an[100][100], min[100];

	cin >> n;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++)
			cin >> an[i][j];
		min[i] = MAX;
	}

	do {
		long key = , key_i;
		flag[now] = 1;
		flag[100] = 0;

		for (int i = 0; i < n; i++) {
			if (an[now][i] != -1 && an[now][i] < min[i] && flag[i] == 0)
				min[i] = an[now][i];
			if (flag[i] == 0 && min[i] < key) {
				key = min[i];
				key_i = i;
			}
			if (flag[i] == 1)
				flag[100]++;
		}

		now = key_i;
		ans += key;

	} while (flag[100] != n - 1);

	cout << ans << endl;

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
struct cww{cww(){ios::sync_with_stdio(false);cin.tie(0);}}star;
#define P(x) cout << (x) << '\n'
#define p(x) cout << (x)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define vv(type, c, m, n, i) vector<vector<type>> c(m, vector<type>(n, i));
#define rep(i,a,n) for(int i=(a), i##_len=(n); i<i##_len; ++i)
#define rrep(i,a,n) for(int i=(a), i##_len=(n); i>i##_len; --i)
#define len(x) ((int)(x).size())
#define mp make_pair
#define eb emplace_back
typedef long long ll;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<long long> vll;
typedef vector<string> vs;
typedef vector<bool> vb;
constexpr int MAX = 101;
constexpr int INF = 1<<21;
enum Color { WHITE = 0, GRAY, BLACK };
int n;
vv(int, M, MAX, MAX, INF);
inline int prim() {
    vi d(n, INF), t(n, -1), color(n, WHITE);
    d[0] = 0;
    int minv, u;
    while(true) {
        minv = INF;
        u = -1;
        rep(i, 0, n) {
            if(minv > d[i] && color[i] != BLACK) {
                u = i;
                minv = d[i];
            }
        }
        if(u == -1) break;
        color[u] = BLACK;
        rep(v, 0, n) {
            if(color[v] != BLACK && d[v] > M[u][v]) {
                d[v] = M[u][v];
                t[v] = u;
                color[v] = GRAY;
            }
        }
    }
    return accumulate(all(d), 0);
}
int main() {
    cin >> n;
    int e;
    rep(i, 0, n) {
        rep(j, 0, n) {
            cin >> e;
            if(e != -1) M[i][j] = e;
        }
    }
    P(prim());
    return 0;
}