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 <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 color(n, WHITE);
	int d[n];
	d[0] = 0;
	rep(i, 1, n) d[i] = INF;
    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];
                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;
}

C++: #include <iostream>

using namespace std;

int n;
int adja[100][100];

int spanning() {
    int visit[100] = {}, cost = 0;
    visit[0] = 1;
    while (1) {
        int minj, minc = 2001;
        for (int i = 0; i < n; ++i) {
            if (visit[i]) {
                for (int j = 0; j < n; ++j) {
                    if (adja[i][j] >= 0 && !visit[j] && minc > adja[i][j]) {
                        minc = adja[i][j];
                        minj = j;
                    }
                }
            }
        }
        if (minc == 2001)
            break;
        cost += minc;
        visit[minj] = 1;
    }
    return cost;
}

int main() {
    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            cin >> adja[i][j];
        }
    }
    cout << spanning() << endl;

    return 0;
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;

int x[10000][10000];
int MIN[10000];
int MINX = 0;
int MINZ = 10000000;

int main() {
	memset(MIN, 127, sizeof(MIN));
	int n, a;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> a;
			x[i][j] = a;
		}
	}
	for(int i=0;i<n;i++){
	    for(int j=0;j<n;j++){
	        if(x[i][j]!=-1){
	            MIN[i]=min(x[i][j],MIN[i]);
	        }
	    }
	}
	for(int i=0;i<n;i++){
	    MINX=0;
	    for(int j=0;j<n;j++){
	        MINX += min[j];
	    }
	    MINZ=min(MINZ,MINX);
	}
	cout<<MINZ<<endl;
	return 0;
}

C++: #include<stdio.h>

static const int MAX = 500;
static const int INFTY = (1<<21);

main(){
  int n, i, j, e, sum,M[MAX][MAX]={0};
  int u,minV,INT_MAX,A[MAX]={INFTY},key[MAX]={INFTY};
  /*

    your code


   */

  scanf("%d", &n);
  
  for ( i = 0; i< n; i++ ){
    for ( j = 0; j < n; j++ ){
      scanf("%d", &e);
      M[i][j] = (e==-1)?INFTY:e;
    }
  }
  
  
  while(1){
    minV = 
      for(i=1;i<=n;i++){
        if((i < minV) && 

  






















  sum = 0;

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

  printf("%d\n", sum);

  retur
}

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

static const int MAX = 100;
static const int INFTY = 3000;
static const int WHITE = 0, GRAY = 1, BLACK = 2;

int n;
int A[MAX][MAX];

int prim() {
	int i1, j1, min;
	int p[MAX], color[MAX], d[MAX];

	for (int i = 0; i < n; i++)	{
		p[i] = -1; //MST??????????????????i??????
		color[i] = WHITE; 
		d[i] = INFTY; //MST??¨????????\????????????????°??????¢
	}
	d[0] = 0;

	while (1) {
		min = INFTY;
		i1 = -1;
		for (int i = 0; i < n; i++)	{
			if (d[i] < min && color[i] != BLACK) {
				i1 = i;
				min = d[i];
			}
		}
		if (i1 == -1) break;

		color[i1] = BLACK;
		for (int j = 0; j < n; j++)	{
			if (A[i1][j] != INFTY && color[j] != BLACK) {
				if (d[j] > A[i1][j]) {
					d[j] = A[i1][j];
					p[j] = i1;
					color[j] = GRAY;
				}
			}
		}
	}
	int sum = 0;
	for (int i = 0; i < n; i++)	{
		if (p[i] != -1) sum += A[i][p[i]];
	}
	return sum;
}

int main() {
	int i1,j1;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int t;
			cin >> t;
			A[i][j] = (t == -1) ? INFTY : t;
		}
	}

	cout << prim() << endl;

	return 0;
}

C++: #include<iostream>

using namespace std;

static const int N = 100;
static const int I=(1<<21);
static const int W= 0;
static const int G =1;
static const int B =2;

int n,M[N][N];

int prim(){
  int u,minv,d[N],p[N],color[N];
  for(int i=0;i<n;i++){
    d[i]=I;
    p[i]=-1;
    color[i]=W;
  }

  d[0]=0;

  while(1){
    minv=I;
    u=-1;
    for(int i=0;i<n;i++){
      if(minv>d[i]&&color[i]!=B){
        u=i;
        minv=d[i];
      }
    }
    if(u==-1)break;
    color[u]=B;
    for(int v=0;v<n;v++){
      if(color[v]!=B&&M[u][v]!=I){
        if(d[v]>M[u][v]){
          d[v]=M[u][v];
          p[v]=u;
          color[v]=G;  
            
            
        }}
    }
  }
  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) ? I : e;
    }
  }

  cout<<prim()<<endl;

  return 0;
}