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<vector>

int main() {
	int num;
	std::cin >> num;

	std::vector<std::vector<int> > v(num);

	for (int i = 0; i < num; i++) {
		for (int j = 0; j < num; j++) {
			int n;
			std::cin >> n;
			v[i].push_back(n);
		}
	}

	std::vector<int> n(v.size(), 0);
	int count = 0;
	for (int i = 1; i <= 2000; i++) {
		for (size_t j = 0; j < v.size(); j++) {
			for (size_t k = 0; k < v.size(); k++) {
				if (v[j][k] == i && (n[j] == 0 || n[k] == 0)) {
					n[j] = n[k] = 1;
					count += i;
				}
			}
		}
	}

	std::cout << count << std::endl;

	return 0;
}

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

const int MAX = 100;

int count(bool check[MAX], int graph[MAX][MAX], int n,int i) {
	check[i] = true;
	int sum = 0;
	for (int j = 0; j < n; j++) {
		if (graph[i][j] != -1 && check[j] == false) {
			sum += count(check,graph, n, j);
			sum += graph[i][j];
		}
	}
	return sum;
}

int main() {
	int n;
	int g;
	int graph[MAX][MAX];

	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> graph[i][j];
		}
	}

	//?§????
	for (int s = 0; s < n; s++) {
		//?????±???
		for (int m = 0; m < n; m++) {
			if (graph[s][m] == -1)continue;
			//??????
			for (int e = 0; e < n; e++) {
				if (graph[s][e] == -1 || graph[m][e] == -1)continue;
				if (graph[s][e] > graph[s][m] + graph[m][e]) {
					graph[s][e] = -1;
				}
			}
		}
	}

	bool check[MAX] = { false };
	cout << count(check, graph, n, 0) << endl;
	return 0;
}

C++: #include <iostream>
using namespace std;
const int INF = 1e9 + 7;
const int MAX_V = 100;

int cost[MAX_V][MAX_V];
int mincost[MAX_V];
bool used[MAX_V];
int V;

int prim() {
    for (int i = 0; i < V; ++i) {
        mincost[i] = INF;
        used[i] = false;
    }

    mincost[0] = 0;
    int res = 0;

    while (true) {
        int v = -1;
        for (int u = 0; u < V; u++) {
            if (!used[u] && (v == -1 || mincost[u] < mincost[v])) v = u;
        }

        if (v == -1) break;
        used[v] = true;
        res += mincost[v];

        for (int u = 0; u < V; u++) {
            if (cost[v][u] < mincost[u]) {
                mincost[u] = cost[v][u];
            }
        }
    }
    return res;
}

int main() {
    cin >> V;
    for (int i = 0; i < V; i++) {
        for (int j = 0; j < V; j++) {
            cin >> cost[i][j];
            if (cost[i][j] == -1) cost[i][j] = INF;
        }
    }
    cout << prim() << 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;

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 <bits/stdc++.h>
using namespace std;
#define INF (1<<30)
#define MAX_N 100
typedef pair<int, int> P;

struct edge{
    int v[2], cost;
    edge(){}
    edge(int v0, int u0, int cost0){
        v[0] = v0; v[1] = u0; cost = cost0;
    }
    bool operator < (const edge &e) const {
        return cost > e.cost;
    }
};

int ans = 0, N;
vector<edge> E[MAX_N];

void prim(){
    bool seen[N];
    fill(seen, seen + N, false);
    priority_queue<edge> todo;
    seen[0] = true;
    for(int i = 0; i < E[0].size(); i++)
        todo.push(E[0][i]);
    while(!todo.empty()){
        edge e = todo.top(); todo.pop();
        if(seen[e.v[1]]) continue;
        ans += e.cost;
        seen[e.v[1]] = true;
        for(int i = 0; i < E[e.v[1]].size(); i++)
            if(!seen[E[e.v[1]][i].v[1]]) todo.push(E[e.v[1]][i]);
    }
}

int main(){
    cin >> N;
    for(int i = 0; i < N; i++)
        for(int j = 0; j < N; j++){
            int cost;
            cin >> cost;
            if(i < j && cost != -1){
                E[i].push_back(edge(i, j, cost));
                E[j].push_back(edge(j, i, cost));
            }
        }
    prim();
    cout << ans << endl;
    return 0;
}

C++: #include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <utility>
using namespace std;
//_____
#define pb push_back
#define fi first
#define se second
#define mkp make_pair
#define rep(i,n) for(int i=0; i<(n); ++i)
#define reps(i,f,n) for(int i=(f); i<=(n); ++i)
#define err(...) fprintf(stderr, __VA_ARGS__)
#define show(x) cerr << #x << ':' << x << endl
#define outl(x) cout << (x) << '\n'
#define FAST() cin.tie(0), ios::sync_with_stdio(false)
typedef pair<int,int> pii;
#define INF 0x3f3f3f3f
//_______
vector<pii> G[102];
bool used[102];

int prim()
{
   priority_queue < pii, vector<pii>, greater<pii> > pq;
   pq.push( mkp(0,0) );
   int sum = 0;

   while( !pq.empty() ){
      const pii  tmp = pq.top(); pq.pop();
      if( used[ tmp.se ]++ )continue;
      sum += tmp.fi;

      rep(j, G[tmp.se].size() )
         pq.push( mkp( G[tmp.se][j].fi, G[tmp.se][j].se ) );
   }
   return (sum);
}

signed main()
{
   FAST();
   int N; cin >> N;

   rep(i, N)rep(j, N){
      int v; cin >> v;
      if( v != -1 ) G[i].pb( mkp(v,j) );
   }
   outl( prim() );
}