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>
#define inf 10000000
using namespace std;
int main(){
  int n,d[101][101],a[101],ans=0,c[101]={};
  cin>>n;
  for(int i=0;i<n;i++)a[i]=inf;
  for(int i=0;i<n;i++)
    for(int j=0;j<n;j++){
      cin>>d[i][j];
      if(d[i][j]==-1)d[i][j]=inf;    
    }
  a[0]=0;
  int s=0;
  while(1){
    c[s]=1;
    ans+=a[s];
    int mn=inf,ns=-1;
    for(int i=0;i<n;i++)
      a[i]=min(a[i],d[s][i]);

    for(int i=0;i<n;i++)
      if(!c[i]&&a[i]<mn)ns=i,mn=a[i];

    if(ns==-1)break;
    s=ns;
  }
  cout<<ans<<endl;
  return 0;
}

C++: #include <stdio.h>
#define rep(i, n) for(int i = 0; i < n; ++i)

int main(void) {
  int n, i, j, ans = 0;
  scanf("%d", &n);
  int a[n][n];
  char f[n];
  rep(i, n) rep(j, n) scanf("%d", &a[i][j]);
  rep(i, n) f[i] = 0;
  f[0] = 1;
  rep(i, n - 1) {
    int min = 10000, minx, miny;
    rep(j, n) {
      rep(k, n) {
        if(f[j] && !f[k] && a[j][k] => 0 && a[j][k] < min) min = a[j][k], minx = j, miny = k;
      }
    }
    ans += min;
    f[miny] = 1;
  }
  printf("%d\n", ans);
  return 0;
}

C++: #include<iostream>

using namespace std;

int n, M[100][100], W = 0, G = 1, B = 2;

int prim () {

    int u, minv, i, v, d[100], p[100], color[100], sum;

    for (i = 0; i < n; i++) {
        d[i] = (1 << 21);
        p[i] = -1;
        color[i] = W;
    }

    d[0] = 0;

    while (1) {

        minv = (1 << 21);
        u = -1;
        for (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 (v = 0; v < n; v++) {
            if (color[v] != B && M[u][v] != (1 << 21)) {
                if (d[v] > M[u][v]) {
                    d[v] = M[u][v];
                    p[v] = u;
                    color[v] = G;
                }
            }
        }

    }

    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;

    cin >> n;

    for (i = 0; i < n; i++) {
        for (j = 0; j < n; j++) {
            cin >> e;
            M[i][j] = (e == -1) ? (1 << 21) : e;
        }
    }

    cout << prim () << endl;

    return 0;

}

C++: #define _GLIBCXX_DEBUG
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define ALL(v) v.begin(), v.end()
typedef long long ll;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#include <bits/stdc++.h>
using namespace std;

#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INF 1000000010

  int n;
  int M[100][100];
  int color[100];
  int d[100];
  int p[100];
  int mincost;

void prim(){
  rep(u,n) color[u]=WHITE;
  rep(u,n) d[u]=INF;
  d[0]=0;
  p[0]=-1;
  
  int u;
  while(1){
    mincost=INF; 
    rep(i,n){
      if(color[i] != BLACK && d[i]<mincost){
        mincost=d[i];
        u=i;
      }
    }
    
    if(mincost==INF) break;
    
    color[u]=BLACK;
    
    rep(v,n){
      if(color[v] != BLACK && M[u][v] != -1){
        if(M[u][v]<d[v]){
          d[v]=M[u][v];
          p[v]=u;
          color[v]=GRAY;
        }
      }
    }
  }
}

int main(){
  cin>>n;
  
  rep(i,n){
    rep(j,n) cin>>M[i][j];
  }
  
  prim();
  int sum=0;
  rep(i,n) sum+=d[i];
  
  cout<<sum<<endl;
  
  return 0;
}

C++: #include<iostream>

using namespace std;

int n, M[100][100], W = 0, G = 1, B = 2;

int prim () {

    int u, minv, i, v, d[100], p[100], color[100], sum;

    for (i = 0; i < n; i++) {
        d[i] = (1 << 21);
        p[i] = -1;
        color[i] = W;
    }

    d[0] = 0;

    while (1) {

        minv = (1 << 21);
        u = -1;
        for (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 (v = 0; v < n; v++) {
            if (color[v] != B && M[u][v] != (1 << 21)) {
                if (d[v] > M[u][v]) {
                    d[v] = M[u][v];
                    p[v] = u;
                    color[v] = G;
                }
            }
        }

    }

    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;

    cin >> n;

    for (i = 0; i < n; i++) {
        for (j = 0; j < n; j++) {
            cin >> e;
            M[i][j] = (e == -1) ? (1 << 21) : e;
        }
    }

    cout << prim () << endl;

    return 0;

}

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

#define INF 100000000

//訪問状態
#define White 0
#define Gray 1
#define Black 2

//Treeの状態を表した隣接行列
int Tree[100][100];
int sum = 0;

int prim(int n){
  int u, minv;
  //d = 見て来たノードの中から出る最小の辺を記録
  //p = MSTにおける頂点の親を記録
  int d[100], p[100], color[100];

  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 && Tree[u][v] != INF){
	if(d[v] > Tree[u][v]){
	  d[v] = Tree[u][v];
	  p[v] = u;
	  color[v] = Gray;
	}
      }
    }
  }

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

  return sum;

}

int main(){
  int n, status;

  cin >> n;

  for(int i = 0 ; i < n ; i++){
    for(int j = 0 ; j < n ; j++){
      cin >> status;

      if(status == -1){
	Tree[i][j] = INF;
      }else{
	Tree[i][j] = status;
      }
    }
  }

  cout << prim(n) << endl;

  return 0;
}