Go: package main

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

type color int

const (
	white color = iota // 未訪問
	mst                // MSTとして確定
)

// 頂点
type node struct {
	matrix   []int // 隣接行列
	minToMst int   // MSTへの重み最小値
	parent   int   // 最小値の相手
	color    color
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n := eGetInt(scanner)

	nodes := make([]node, n)
	for i := 0; i < n; i++ {
		nodes[i].matrix = eAtoi((strings.Fields(eGetline(scanner))))
		nodes[i].parent = -1
		nodes[i].minToMst = math.MaxInt16
		nodes[i].color = white
	}

	// 初回はnode[0]がMSTに入るように,minToMstを設定
	nodes[0].minToMst = 0
	for { // 全部チェックするまで

		// どの頂点を新たにMSTに取り込むか
		min := math.MaxInt16
		u := -1
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].minToMst < min {
				u = i
				min = nodes[i].minToMst
			}
		}

		if u == -1 {
			break
		}
		// MSTに追加する頂点決定
		nodes[u].color = mst

		// MSTに属していない頂点それぞれについて,MSTとの最小の重みを更新
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].matrix[u] == -1 {
				// 接してない
				continue
			}
			if nodes[i].matrix[u] < nodes[i].minToMst {
				// node[u]との重みが最小
				nodes[i].minToMst = nodes[i].matrix[u]
				nodes[i].parent = u
			}
		}
	}

	sum := 0
	for _, v := range nodes {
		// node[0]はparentが入っていない
		if v.parent != -1 {
			sum += v.matrix[v.parent]
		}
	}
	fmt.Println(sum)
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

C++: #include <iostream>
#include <vector>
#include <queue>
#define to first
#define cost second
const int inf=1e9+7;
using namespace std;
int main(){

  int n,tmp,r=0,flag[100]={},v=0;
  cin>>n;
  vector <pair<int,int> > gl[n];
  priority_queue <pair<int,int> ,vector<pair<int,int> >, greater<pair<int,int> > >q;
  //for(int i=1;i<n;i++) mincost[i]=inf;                                                                                                                                                       

  for(int i=0;i<n;i++) for(int j=0;j<n&&cin>>tmp;j++) if(tmp!=-1) gl[i].push_back(make_pair(j,tmp));
  int now=0;
  for(int j=0;j<n-1;j++){
    for(int i=0;i<gl[now].size();i++) if(!flag[gl[now][i].to]) q.push(make_pair(gl[now][i].cost,gl[now][i].to));
    flag[now]=1;
    //for(;flag[q.top().second];) q.pop();                                                                                                                                                     
    //if(q.empty()) break;                                                                                                                                                                     
    r+=q.top().first;
    now=q.top().second;
    q.pop();
  }
  cout<<r<<endl;
  return 0;

}

C++: //ALDS1_12A
#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(true){
  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(){
 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) ? INF:e;
  }
 }
 cout<<prim()<<endl;
 return 0;
}

C++: #include <iostream>

using namespace std;

static const int MAX = 100;
static const int INF = 1 << 30;
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 (true){
        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()
{
    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) ? INF : e;
        }
    }
    cout << prim() << endl;

    return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vi = vector<int>;
using vvi = vector<vi>;
using vs = vector<string>;
using msi = map<string, int>;
using mii = map<int, int>;
using psi = pair<string, int>;
using pii = pair<int, int>;
using vlai = valarray<int>;
#define rep(i,n) for(int i=0;i<n;i++)
#define range(i,s,n) for(int i=s;i<n;i++)
#define all(a) a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define fs first
#define sc second
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define INF 1E9
#define EPS 1E-9
#define MOD (1E9+7)
#define PI 3.1415926535897932384

std::ostream &operator<<(std::ostream &out, const vector<int> &tgt)
{
	string s;
	for (int i = 0; i<tgt.size(); i++) {
		s += (to_string(tgt[i]) + ((i != tgt.size() - 1) ? " " : ""));
	}
	out << s;
	return out;
}

vvi cost;
int n;

ll prim() {

	//O(n^2)

	vi mincost(n,INF);
	mincost[0] = 0;
	ll res = 0;
	vector<bool> used(n,false);

	while (1) {
		int v = -1;
		rep(i, n) {
			if (!used[i] && (v == -1 || mincost[i] < mincost[v]))v = i;
		}
		if (v == -1)break;
		used[v] = true;
		res += mincost[v];
		rep(i, n) {
			mincost[i] = min(mincost[i], cost[v][i]);
		}
	}
	return res;
}

int main() {
	int in;
	cin >> n;
	rep(i, n) {
		vi tmp;
		rep(j, n) {
			cin >> in;
			tmp.push_back((in!=-1?in:INF));
		}
		cost.push_back(tmp);
	}
	cout << prim() << endl;
}