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 <set>
#include <vector>
#define FOR(i,k,n) for (int (i)=(k); (i)<(n); ++(i))
#define REP(i,n) FOR(i,0,n)
#define pb push_back
#define mp make_pair
#define fst first
#define snd second
#define all(v) begin(v), end(v)
using namespace std;
typedef pair<int,int> PII;

int P[100]; //union_find

int root(int i){
    if(P[i] == i) return i;
    else return P[i] = root(P[i]);
}

bool same(int x, int y){
    return root(P[x]) == root(P[y]);
}

void unite(int x, int y){
    P[root(x)] = root(y);
}

int main(){
    int n;
    cin >> n;
    int g[n][n];
    vector<pair<int,PII>> V;
    REP(i,n){
        REP(j,n){
            cin >> g[i][j];
            if(i<j && g[i][j] >= 0) V.pb(mp(g[i][j],mp(i,j)));
        }
    }
    sort(all(V));
    REP(i,n){
        P[i] = i;
    }
    int wsum=0;
    REP(i,n-1){
        int x = V[i].snd.fst;
        int y = V[i].snd.snd;
        if(!same(x,y)){
            unite(x,y);
            wsum += V[i].fst;
        }
    }

    cout <<wsum<<endl;

    return 0;
}

C++: #include<stdio.h>
#define MAX 100
#define INFTY 2097152
#define WHITE 0
#define GRAY 1
#define BLACK 2
int prim();
int n,M[MAX][MAX];

int main(){
  int e;
  scanf("%d",&n);
  for(int i=0;i<n;i++){
    for(int 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;
}

int prim(){
  int u,minv;
  int d[MAX],p[MAX],color[MAX];
  int sum=0;
  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;
	}
      }}}

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

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<iostream>
using namespace std;

//#include "stdio.h"

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

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

int prim(){
  int sum=0;

  for(int i=0;i<n;i++){
    color[i] = WHITE;
    d[i] = INFTY;
    p[i] = -1;
  }

  d[0] = 0;
  p[0] = -1;

  while(true){
    int u=-1;
    int minicost=INFTY;

    for(int i=0;i<n;i++){
      if( color[i] != BLACK && minicost > d[i] ){
        minicost = d[i];
        u = i;
      }
    }
    if(u==-1){
      break;
    }
    color[u] = BLACK;

    for(int v=0;v<n;v++){
      if(color[v] != BLACK && d[v] > M[u][v]){
        d[v] = M[u][v];
        p[v] = u;
        color[v] = GRAY;
      }
    }
  }

  for(int i=0;i<n;i++){
    sum = sum + d[i];
  }

  return sum;
}


int main(void){

  cin >> n;

  int weight;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      cin >> weight;
 
      if(weight == -1){
        M[i][j] = INFTY;
      }else{
        M[i][j] = weight;
      }
    }
  }

  cout << prim() << endl;

  return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
#define INF 1<<30
#define MAX_V 100

int n;
int M[MAX_V][MAX_V];
bool added[MAX_V];
int d[MAX_V], p[MAX_V];

int prim(){
  for(int i = 0; i < n; i++){
    d[i] = INF;
    added[i] = false;
  }

  d[0] = 0; p[0] = -1;

  while(true){
    int minCost = INF, u;
    for(int i = 0; i < n; i++){
      if(!added[i] && d[i] < minCost){
        minCost = d[i];
        u = i;
      }
    }

    if(minCost == INF) break;

    added[u] = true;

    for(int i = 0; i < n; i++){
      if(!added[i] && M[u][i] != -1 && M[u][i] < d[i]){
        d[i] = M[u][i];
        p[i] = u;
      }
    }
  }
  
  int 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++){
    cin >> M[i][j];
  }
  cout << prim() << endl;
  return 0;
}