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<algorithm>
using namespace std;
#define MAX_E 100005
#define MAX_V 10005

struct edge{int u, v, cost;};

bool comp(const edge& e1, const edge& e2){
	return e1.cost < e2.cost;
}
int V, E;
edge es[MAX_E];
int par[MAX_V];
int _rank[MAX_V];

void init(int x){
	for(int i = 0; i < x; i++){
		par[i] = i;
		_rank[i] = 0;
	}
}

int find(int x){
	return par[x] == x ? x : par[x] = find(par[x]);
}

void unite(int x, int y){
	x = find(x);
	y = find(y);
	
	if(_rank[x] < _rank[y]){
		par[x] = y;
	} else{
		par[y] = x;
		if(_rank[x] == _rank[y]) _rank[x]++;
	}
}

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

int kruskal(){
	sort(es, es + E, comp);
	init(V);
	int res = 0, count = 0;
	for(int i = 0; i < E; i++){
		edge e = es[i];
		if(!same(e.u, e.v)){
			unite(e.u,e.v);
			res += e.cost;
			count++;
		}
	}
	return res;
}

int main(){
	int s, t, w, x, y = 0;
	
	cin>>V;
	
	for(int i = 1; i <= V; i++){
		for(int j = 1; j <= V; j++){
			cin>>x;
			if(x != -1 && i <= j){
				es[y].u = i;
				es[y].v = j;
				es[y++].cost = x;
			}
		}
	}
	
	E = y;
	
	cout<<kruskal()<<endl;
	
	return 0;
	
}

C++: #include <iostream>
using namespace std;
static const int MAX = 100, INFTY = (1 << 21), WHITE = 0, GRAY = 1, BLACK = 2;

int N, M[MAX][MAX];

int prim() {
	int u, minv;
	int D[MAX], P[MAX], C[MAX];

	for (int i = 0; i < N; i++) {
		D[i] = INFTY;
		P[i] = -1;
		C[i] = WHITE;
	}

	D[0] = 0;
	while (true) {
		minv = INFTY;
		u = -1;
		for (int i = 0; i < N; i++) {
			if (minv > D[i] && C[i] != BLACK) {
				u = i;
				minv = D[i];
			}
		}
		if (u == -1) break;
		C[u] = BLACK;
		for (int v = 0; v < N; v++) {
			if (C[v] != BLACK && M[u][v] != INFTY) {
				if (D[v] > M[u][v]) {
					D[v] = M[u][v];
					P[v] = u;
					C[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;
}

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
#include <queue>
#include <stack>
#include <map>
#define FOR(i,b,e) for(int i=b;i<e;i++)
#define REP(i,n) FOR(i,0,n)
#define INFTY 1000000
using namespace std;

const int N = 100;
int n;
int D[N], M[N][N];
bool V[N];

int prim() {
  int nn, minD, cost;

  REP(i, n) D[i] = INFTY;
  D[0] = 0;

  while (true) {
    minD = INFTY;
    REP(i, n) {
      if (!V[i] && D[i] < minD) {
        minD = D[i];
        nn = i;
      }
    }
    if (minD == INFTY) break;

    cost += D[nn];
    V[nn] = true;
    REP(i, n) {
      if (!V[i] && M[nn][i] != -1 && M[nn][i] < D[i]) {
        D[i] = M[nn][i];
      }
    }
  }

  return cost;
}

int main() {
	cin.tie(0);
 	ios::sync_with_stdio(false);

  cin >> n;
  REP(i, n) {
    REP(j, n) {
      cin >> M[i][j];
    }
  }

  cout << prim() << endl;
}

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

struct UF{
   vector<int> par;
   vector<int> sz;
   UF(){}
   UF(int n){
       par.resize(n);
       sz.resize(n, 1);
       for(int i = 0; i < n; i++) par[i] = i;
   }
   int find(int x){
       if(x == par[x]) return x;
       return par[x] = find(par[x]);
   }
   void unite(int x, int y){
       x = find(x); y = find(y);
       if(x == y) return;
       if(sz[x] < sz[y]) swap(x, y);
       sz[x] += sz[y];
       par[y] = x;
   }
   bool same(int x, int y){
       return find(x) == find(y);
   }
};

struct edge{
    int u, v, cost;
    bool operator<(const edge &e) const{
        return cost < e.cost;
    }
};

int n, m;
vector<edge> es; 

int kruskal(){
    int res = 0;    
    UF uf(n);
    sort(es.begin(), es.end());
    for(int i = 0; i < m; i++){
        edge e = es[i];
        if(!uf.same(e.u, e.v)){
            uf.unite(e.u, e.v);
            res += e.cost;
        }
    }
    return res;
}

int main(){
    cin >> n;
    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            int in;
            cin >> in;
            if(in == -1) continue;
            es.push_back({i, j, in});
        }
    }
    m = es.size();
    cout << kruskal() << endl;
}

C++: # include <iostream>
using namespace std;
const int MAXN = 1000;
int main(void)
{
	int d[MAXN],a[MAXN][MAXN],vis[MAXN],p[MAXN];
	int n,ans = 0,cnt = 0;
	scanf("%d",&n);
	for(int i = 0;i < n;i++) for(int j = 0;j < n;j++) scanf("%d",&a[i][j]);
	for(int i = 0;i < n;i++)
	{
		vis[i] = 0;
		p[i] = -1;
		d[i] = 2001;
	}
	d[0] = 0;
	while(true)
	{
		int u = -1,minv = 2001;
		for(int i = 0;i < n;i++)
		{
			if(d[i] < minv && !vis[i])
			{
				u = i;
				minv = d[i];
			}	
		}
		if(u == -1) break;
		cnt++;
		vis[u] = 1;
		for(int v = 0;v < n;v++)
		{
			if(!vis[v] && a[u][v] != -1)
			{
				if(d[v] > a[u][v])
				{
					d[v] = a[u][v];
					p[v] = u;
				}
			}
		}
	}
	for(int i = 0;i < n;i++) if(p[i] != -1) ans += a[i][p[i]];
	printf("%d\n",(cnt == n)?ans:-1);
	return 0;
}