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 "stdio.h"

#define MAX 100
#define INFTY 1<<21
#define WHITE 0
#define GRAY 1
#define BLACK 2

int n, M[MAX][MAX];

int prim(){
  int i, v;
  int u, minv;
  int d[MAX], p[MAX], color[MAX];

  for(i=0; i<n; i++){
    d[i] = INFTY;
    p[i] = -1;
    color[i] = WHITE;
  }
  d[0] = 0;
  while (1) {
    minv = INFTY;
    u = -1;
    for(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(i=0; i<n; i++)
  if(p[i]!=-1) sum += M[i][p[i]];

  return sum;
}

int main(){
  int i, j, e;
  scanf("%d", &n);
  for(i=0; i<n; i++){
    for(j=0; j<n; j++){
      scanf("%d", &e);
      if(e == -1){
        M[i][j] = INFTY;
      }else{
        M[i][j] = e;
      }
    }
  }
  printf("%d\n", prim());

  return 0;

}

C++: #include<iostream>
using namespace std;
static const int M = 100;
static const int INF = (1<<21);
static const int W = 0;
static const int G = 1;
static const int B = 2;

int n, m[M][M];

int prim() {
	int u, minv,sum=0;
	int i,v,d[M], p[M], c[M];

	for (i = 0; i < n; i++) {
		d[i] = INF;
		p[i] = -1;
		c[i] = W;
	}
	d[0] = 0;
	while (1) {
		minv = INF;
		u = -1;
		for (i = 0; i < n; i++) {
			if (minv > d[i] && c[i] != B) {
				u = i;
				minv = d[i];
			}
		}
		if (u == -1) {
			break;
		}
		c[u] = B;
		for (v = 0; v < n; v++) {
			if (c[v] != B && m[u][v] != INF) {
				if (d[v] > m[u][v]) {
					d[v] = m[u][v];
					p[v] = u;
					c[v] = G;
				}
			}
		}
	}
	for (i = 0; i < n; i++) {
		if (p[i] != -1) {
			sum += m[i][p[i]];
		}
	}
	return sum;
}

int main(void) {
	int i,j,e;
	cin >> n;
	for (i = 0; i < n; i++) {
		for (j = 0; j < n; j++) {
			cin >> e;
			m[i][j] = (e == -1) ? INF : e;
		}
	}
	cout << prim() << endl;
	return 0;
}

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

struct edge{ int a,b,cost; };

int parent[100],height[100];

bool comp(const edge& e1,const edge& e2){
	return e1.cost < e2.cost;
}

int find(int x){
	if(parent[x] == x) return x;
	else return parent[x] = find(parent[x]);
}

void unite(int x,int y){
	x = find(x);
	y = find(y);
	if(x == y) return;
	if(height[x] < height[y]){
		parent[x] = y;
	}else {
		parent[y] = x;
		if(height[x] == height[y]) height[x]++;
	}
}

bool same(int x,int y){
	return find(x) == find(y);
}

int main(){
	int n,res = 0;
	cin >> n;
	vector<edge> es;
	for(int i = 0;i < n;i++) parent[i] = i;
	for(int i = 0;i < n;i++){
		for(int j = 0;j < n;j++){
			int t;
			cin >> t;
			if(t != -1) es.push_back({i,j,t});
		}
	}
	sort(es.begin(),es.end(),comp);
	for(int i = 0;i < es.size();i++){
		edge e = es[i];
		if(!same(e.a,e.b)){
			unite(e.a,e.b);
			res += e.cost;
		}
	}
	cout << res;
	return 0;
}

C++: #include <utility>
#include <string>
#include <vector>
#include <algorithm>
#include <iostream>
using namespace std;

int n;
int a[100][100] = {0};
int f[100] = {0};
int c = -1;

int kansu( int i, int t, int s ){
	f[i] = s;
	t++;
	if ( t != n ) {
		for ( int j = 0; j < n; j++ ) {
			if ( a[i][j] != -1 && f[j] == -1 ) kansu( j, t, s + a[i][j] );
		}
	}else {
		if ( c == -1 || c > s ) c = s;
	}
	f[i] = -1;
	return 0;
}

int main(){
	cin >> n;
	int s;
	for ( int i = 0; i < n; i++ ) {
		for ( int j = 0; j < n; j++ ) {
			cin >> a[i][j];
		}
		f[i] = -1;
	}
	for ( int i = 0; i < n; i++ ) {
		kansu(i,0,0);
	}
	cout << c << 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;

struct Node{
  int color, dist, parent;
};

int n, M[MAX][MAX];
Node node[MAX];

void Printnodes(){
  string col[3] = {"WHITE", "GRAY ", "BLACK"};
  for(int i = 0; i < n; i++){
    cout << "nodeID : " << i ;
    cout << " color : " << col[node[i].color];
    cout << " parent : " << node[i].parent;
    cout << " dist : " << node[i].dist << endl;
  }
  cout << endl;
}

int main(){
  cin >> n;

  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> M[i][j];
    }
    node[i].color = WHITE;
    node[i].dist = INFTY;
    node[i].parent = -1;
  }

  int p = 0;
  node[p].dist = 0;

  while(true){
    //Printnodes();

    for(int i = 0; i < n; i++){
      if(M[p][i] > 0 && node[i].color != BLACK){
        if(node[i].dist > M[p][i]){
          node[i].dist = M[p][i];
          node[i].parent = p;
          node[i].color = GRAY;
        }
      }
    }

    int min_d = INFTY;
    p = -1;
    for(int i = 0; i < n; i++){
      if(node[i].dist < min_d && node[i].color != BLACK){
        min_d = node[i].dist;
        p = i;
      }
    }

    if(p == -1)
      break;

    node[p].color = BLACK;
    //cout << "node " << p << " turns to BLACK!" << endl;
  }

  int sum = 0;

  for(int i = 0; i < n; i++){
    if(node[i].parent >= 0)
      sum += M[i][node[i].parent];
  }
  cout << sum << endl;
  return 0;
}