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 P pair<int,int>
using namespace std;

int a[100][100];
bool used[100];
signed main(){
	int b; cin >> b;
	for (int c = 0; c < b; c++) {
		for (int d = 0; d < b; d++) {
			cin >> a[c][d];
			if (a[c][d] == -1) {
				a[c][d] = INT_MAX / 3;
			}
		}
	}
	int ans = 0;
	priority_queue<P,vector<P>, greater<P>>Q;
	Q.push({ 0,0 });
	while (Q.size()) {
		P t = Q.top(); Q.pop();
		if (!used[t.second]) {
			ans += t.first;
			used[t.second] = true;
			for (int i = 0; i < b; i++) {
				Q.push({ a[t.second][i],i });
			}
		}
	}
	cout << ans << endl;
}

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;

static const int MAX = 100;
static const int NIL = (1 << 21);
static const int WHITE = 0;
static const int GREY = 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] = INFY;
    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; i < n; i++) {
      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>
#define INF 2000000
#define MAX 100
#define WHITE 0
#define BLACK 1

using namespace std;

int n, d[MAX], color[MAX], w[MAX][MAX];

void prim(int r){
    int u;
    for(u = 0; u < n; u++){
        d[u] = INF;
        color[u] = WHITE;
    }
    d[r] = 0;

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

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

int main(){
    int i, j;
    cin >> n;
    for(i = 0; i < n; i++){
        for(j = 0; j < n; j++){
            cin >> w[i][j];
            if(w[i][j] == -1) w[i][j] = INF;
        }
    }

    prim(0);

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

C++: #include<iostream>
#include<algorithm>
using namespace std;
int p[101],r[101];
void makeset(int x){
    for(int i=0;i<x;++i){
        p[i]=i;
        r[i]=0;
    }
}
int root(int a){
    if(a!=p[a])
        p[a]=root(p[a]);
    return p[a];
}
bool same(int a,int b){
    return (root(a)==root(b));
}
void link(int a,int b){
    if(r[a]>r[b]){
        p[b]=a;
    }
    else{
        p[a]=b;
        if(r[a]==r[b]){
            r[b]++;
        }
    }
}
void unite(int a,int b){
    link(root(a),root(b));
}
struct Edges{int cost,src,dst;}edges[10010];
bool operator<(const Edges &x,const Edges &y){return x.cost<y.cost;}
int main(){
    int N,M=0;
    int A[101][101];
    cin>>N;
    makeset(N);
    for(int r=0;r<N;++r){
        for(int c=0;c<N;++c){
            cin>>A[r][c];
        }
        for(int c=r+1;c<N;++c){
            if(A[r][c]>-1){
                edges[M].cost=A[r][c];
                edges[M].src=r;
                edges[M].dst=c;
                M+=1;
            }
        }
    }
    sort(edges,edges+M);
    int total=0,num=0,flag=0;
    for(int i=0;i<M;++i){
        if(same(edges[i].src,edges[i].dst)){continue;}
        else{
            unite(edges[i].src,edges[i].dst);
            total+=edges[i].cost;
            num++;
        }
        if(num==N-1){
            flag=1;
            break;
        }
    }
    if(flag){
        cout<<total<<endl;
    }
}