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 <string>
#include <algorithm>
#include <cstdio>
#include <vector>
#include <queue>
#include <set>
#include <numeric>
#include <cmath>

using namespace std;

typedef long long int lld;

const lld mod = 1e9+7;
const lld INF = 1e9;
//const lld MAXN = 1e9;

struct edge
{
	int cost,u,v;
	bool operator<(const edge& e) const
	{
		return cost < e.cost;
	}
};

int main()
{
	int n,a[100][100] = {0};

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

	vector<edge>  e;

	for(int i = 0; i < n; i++)
	{
		for(int j = i; j < n; j++)
		{
			if (a[i][j] >= 0)
			{
				edge f;
				f.cost = a[i][j];
				f.u = i;
				f.v = j;
				e.push_back(f);
			}
		}
	}

	sort(e.begin(),e.end());

	set<int> span;
	int sol = 0;

	for(int i = 0; i < e.size(); i++)
	{
		if (!span.count(e[i].u) || !span.count(e[i].v))
		{
			sol += e[i].cost;
			span.insert(e[i].u);
			span.insert(e[i].v);
		}
	}

	cout << sol << endl;

	return 0;
}

C++: //Minimu Spanning Tree
#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];

long prim(){
    int u, minv;
    int d[MAX], p[MAX], color[MAX];
    
    //d is INF, p is -1, color IS WHITE;
    for(int i = 0; i < n; i++){
        d[i] = INF;
        p[i] = -1;
        color[i] = WHITE;
    }
    //cost of start point is zero.
    d[0] = 0;
    
    while(true){
        minv = INF;
        u = -1;
        
        //????°???¨????????????V - S????????¢???????????????S?????£??\??????????????????
        for(int i = 0; i < n; i++){
            if(minv > d[i] && color[i] != BLACK){
                minv = d[i];
                u = i;
            }
        }
        
        //???????????????????????¨????????????????????????S=V??¨?????£???
        if(u == -1) break;
        
        color[u] = BLACK;
        for(int v = 0; v < n; v++){
            if(color[v] != BLACK && M[u][v]){
                if(M[u][v] < d[v]){
                    d[v] = M[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }
    
    long sum = 0;
    for(int i = 0; i < n; i++){
        if(p[i] != -1) sum += M[i][p[i]];
    }
    
    return sum;
    
}

int main(void){
    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>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <cctype>
#include <string>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>
#include <functional>

using namespace std;
using ll = long long int;
#define rep(i,n) for(int i = 0; i < n; i++)
#define FOR(i, a, b)  for(int i = (a); i < (b) ; i++)

#define pb push_back
#define SORT(v,n) sort(v, v+n)
#define ALL(x) (x).begin(),(x).end()
#define debug(x) cerr << #x << ": " << x << '\n'
#define elif else if
#define itn ll
#define int ll
const int INF = 100100100;
const int MOD = (int)1e9 + 7;
const double EPS = 1e-9;
///                →,↑,←,↓,↗,↖,↙,↘
int dx[8] = { 1, 0, -1, 0, 1, -1, -1, 1 };
int dy[8] = { 0, 1, 0, -1, 1, 1, -1, -1 };

static const int MAX = 100;
static const int White = 0;
static const int Gray = 1;
static const int Black = 2;

int n, M[MAX][MAX],color[MAX];

int prim() {
	int d[MAX], p[MAX];
	int i,sum = 0;
	rep(i, n) {
		d[i] = INF;
		p[i] = -1;
		color[i] = White;
	}
	d[0] = 0;
	while (true) {
		int u = -1;
		int minv = INF;
		rep(i, n) {
			if (color[i] != Black && d[i] < minv) {
				minv = d[i];
				u = i;
			}
		}
		if (u == -1)
			break;
		color[u] = Black;
		int v;
		rep(v, n) {
			if (color[v] != Black && M[u][v] != INF) {
				color[v] = Gray;
				d[v] = M[u][v];
				p[v] = u;
			}
		}
	}
	rep(i, n) {
		if (p[i] != -1) {
			sum += M[i][p[i]];
		}
	}
	return sum;
}

signed main() {
	ios::sync_with_stdio(false);
	cin >> n;
	int i,j;
	rep(i, n) {
		rep(j, n) {
			int a;
			cin >> a;
			M[i][j] = (a == -1) ? INF : a;
		}
	}
	cout << prim() << '\n';
	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];

  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 <bits/stdc++.h>
#define INF 2001
using namespace std;
int M[100][100],d[100],p[100];
bool vist[100]={0};
void prim(int n){
	for(int i=0;i<n;i++) d[i] = INF;
	d[0] = 0;
	p[0] = -1;
	int mincost, u;
	while(1){
		mincost = INF;
		for(int i=0;i<n;i++)
			if(!vist[i] && d[i]<mincost)
				mincost = d[i], u = i;
		if(mincost == INF) break;
		vist[u] = 1;
		for(int i=0; i<n; i++)
			if(!vist[i] && M[u][i]!=-1 && M[u][i]<d[i])
				d[i] = M[u][i],
				p[i] = u;
	}
}
int main()
{	int n; cin>>n;
	for(int i = 0;i < n;i++)
		for(int j = 0;j < n;j++)
			scanf("%d",&M[i][j]);
	prim(n);
	long long ans = 0;
	for(int i=1; i<n; i++)
		ans += M[i][p[i]];
	cout << ans << endl;
	return 0;
}