Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

const BIG_COST = 3000

const (
	ST_NOT_YET = iota
	ST_JOINED
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	costs := make([][]int, nNodes)

	for r := 0; r < nNodes; r++ {
		costs[r] = make([]int, nNodes)
		for c := 0; c < nNodes; c++ {
			costs[r][c] = scanInt(sc)
		}
	}

	states := make([]int, nNodes)
	minCosts := make([]int, nNodes)

	for i := 1; i < nNodes; i++ {
		minCosts[i] = BIG_COST
	}

	for {
		var u int
		minCost := BIG_COST

		for i := 0; i < nNodes; i++ {
			if states[i] != ST_JOINED && minCosts[i] < minCost {
				minCost = minCosts[i]
				u = i
			}
		}

		// 全てのノードが MST に JOIN できたので終了。
		if minCost == BIG_COST {
			break
		}

		states[u] = ST_JOINED

		for v := 0; v < nNodes; v++ {
			cost := costs[u][v]

			// MST内の u と MST外の v との辺の重みをそれぞれ minCosts[v] として
			// 保存しておく。このうち辺の重みが最小となる v が次のループで MST に JOIN する。
			if states[v] != ST_JOINED && cost != -1 && cost < minCosts[v] {
				minCosts[v] = cost
			}
		}
	}

	sum := 0
	for _, cost := range minCosts {
		sum += cost
	}
	fmt.Println(sum)
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

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

#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INF 2000000000

int x[10000][10000];
int color[10000];
int MIN[10000];
int sum;
int sum_min = INF;

int main() {
	int n, a, b, c;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> x[a][b];
		}
	}
	for (int i = 0; i < n; i++) {
		memset(MIN, 0, sizeof(MIN));
		b = INF;
		a = 1;
		color[i] = GRAY;
		MIN[i] = 0;
		while (a >= 1) {
			for (int j = 0; j < n; j++) {
				if (color[j] = GRAY) {
					if (b > MIN[j]) {
						b = MIN[j];
						c = j;
					}
				}
			}
			color[c] = BLACK;
			a -= 1;
			for (int j = 0; j < n; j++) {
				if (color[j] != BLACK && x[c][j] != -1) {
					if (color[i] == WHITE) {
						a += 1;
					}
					color[j] = GRAY;
					MIN[j] = min(x[c][j], MIN[j]);
				}
			}
		}
		sum = 0;
		for (int j = 0; j < n; j++) {
			sum += MIN[j];
		}
		sum_min = min(sum_min, sum);
	}
	cout << sum_min << endl;
	return 0;
}

C++: #include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;


struct Unionfind{
    vector<int> parents;
    int n;
    Unionfind(int n):n(n),parents(n,-1){ }

    int find(int x){
        if(parents[x] < 0) return x;
        else return parents[x] = find(parents[x]);
    }

    void unite(int x,int y){
        x = find(x);
        y = find(y);

        if(x==y) return;
        if(parents[x] > parents[y]) swap(x,y);
        parents[x] += parents[y];
        parents[y] = x;
    }  

   int size(int x){
       return -parents[find(x)];
   }

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

   vector<int> members(int x){
       int root = find(x);
       vector<int> member;
       for(int i=0;i<n;i++){
           if(find(i)==root){
               member.push_back(i);
           }
       }
      return member;
  }

  int group_cnt(){
      int c = 0;
      rep(i,n){
          if(parents[i] < 0) ++c;
      }
      return c;
  }
};

struct edge{
    int from,to,cost;  
};

int main(){
    int n;
    cin >> n;
    vector<edge> eg;
    rep(i,n)rep(j,n){
        int a;
        cin >> a;
        if(i > j) continue;
        if(a==-1) continue;
        eg.push_back(edge{i,j,a});
    }

    sort(eg.begin(),eg.end(),[](const edge &l,const edge &r){
        return l.cost < r.cost;
    });

    Unionfind uf(n);
    int ans = 0;

    rep(i,eg.size()){
        if(uf.same(eg[i].from,eg[i].to)) continue;
        uf.unite(eg[i].from,eg[i].to);
        ans += eg[i].cost;
    }
    
    cout << ans << endl;
    return 0;
}

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

#define INF 1000000
#define N_MAX 100
#define WH 0
#define GR 1
#define BK 2

int main() {
    int n;
    cin >> n;
    int A[N_MAX][N_MAX] = {};
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            int a;
            cin >> a;
            if (a == -1) {
                A[i][j] = INF;
            }
            else {
                A[i][j] = a;
            }
        }
    }

    int color[N_MAX] = {};
    int d[N_MAX];
    for (int i = 0; i < n; i++) {
        d[i] = INF;
    }
    int p[N_MAX] = {};

    while (true) {
        int u;
        int min_cost = INF;
        d[0] = 0;
        p[0] = -1;

        for (int i = 0; i < n; i++) {
            if (color[i] != BK && d[i] < min_cost) {
                min_cost = d[i];
                u = i;
            }
        }
        if (min_cost == INF) {
            break;
        }
        color[u] = BK;

        for (int v = 0; v < n; v++) {
            if (color[v] != BK && A[u][v] != INF) {
                if (A[u][v] < d[v]) {
                    d[v] = A[u][v];
                    p[v] = u;
                    color[v] = GR;
                }
            }
        }
    }

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

    return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <queue>
#include <utility>

using namespace std;

const int NIL = 2001;
const int MAX = 100;
int G[MAX][MAX];
int W[MAX];
int n;

void MST() {
	priority_queue<pair<int, int>> PQ;
	PQ.push(make_pair(0, 0));
	W[0] = 0;
	while (!PQ.empty()) {
		int u = PQ.top().second;
		PQ.pop();
		for (int i = 0; i < n; ++i) {
			if (G[u][i] != -1 && G[u][i] < W[i]) {
				PQ.push(make_pair(G[u][i] * -1, i));
				W[i] = G[u][i];
			}
		}
	}
}

int main() {

	scanf("%d", &n);
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j)
			G[i][j] = NIL;
		W[i] = NIL;
	}

	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			int a;
			scanf("%d", &a);
			G[i][j] = a;
		}
	}

	MST();

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

	return 0;
}

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

int n;
const int INF = 100100100;

int a[105][105];

int u,minv;
int d[105],p[105],color[105];

int prim(){

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

  while(1){
    minv = INF;
    u = -1;
    for(int i = 0; i < n; i++){
      if(minv > d[i] && color[i] != 2){
        minv = d[i];
        u = i;
      }
    }
    if(u==-1) break;

    color[u] = 2;

    for(int i = 0; i < n; i++){
      if(color[i]!= 2 && a[u][i] != INF){
        if(d[i] > a[u][i]){
          d[i] = a[u][i];
          p[i] = u;
          color[i] = 1;
        }
      }
    }
  }
  int sum = 0;
  for(int i = 0; i < n; i++){
    if(p[i] != -1) sum+=a[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;
      a[i][j] = (e == -1) ? INF:e;
    }
  }
  cout << prim() << endl;
  return 0;
}