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 <utility>
#include <string>
#include <algorithm>
#include <set>
#include <deque>
#include <vector>
#define MAX 150
#define rep(i,p) for(int i=0;i<p;i++)
#define rep1(i,p) for(int i=1;i<=p;i++)
#define pb push_back
using namespace std;
int n,temp,a,b;
int A[MAX];
int B[MAX];
int W[MAX];
int V[MAX];
pair<int,int> edge[MAX];
int main(){
  cin >> n;
  rep(i,n) 
    rep(j,n) {
      int nnn = i*n + j;
      cin >> W[nnn];
      A[nnn] = i;
      B[nnn] = j;
      edge[nnn].first = W[nnn];
      edge[nnn].second = nnn;
  }
  // sort by lenght of edge
  sort(edge, edge+n*n);
  // printing
  // rep(i,n*n) {
  //   cout << A[edge[i].second] << " " << B[edge[i].second]
  //        << " " << edge[i].first << endl;;
  // }
  int sum = 0;
  rep(i,n) V[i] = i;
  rep(i,n*n) {
    if (edge[i].first == -1) continue;
    temp = edge[i].second;
    // a , b : vertex
    a = A[temp]; 
    b = B[temp];
    if (V[a] != V[b]) {
      // ?????????????????????
      sum += edge[i].first;
      if (V[a] != a && V[b] == b){
        V[b] = V[a];
      } else if (V[a] == a && V[b] != b) {
        V[a] = V[b];
      } else if (V[a] == a && V[b] == b) {
        V[b] = V[a];
      }
    } else {

    }
  }
  cout << sum << endl;
  return 0;
}

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

#define MAX_SIZE 110
#define INF (1<<30)
#define NOT_VISITED 0
#define VISITED 1
#define COMPLETE 2

int n, G[MAX_SIZE][MAX_SIZE];

int prim() {
    int d[MAX_SIZE], parent[MAX_SIZE], status[MAX_SIZE];
    for (int i = 0; i < n; i++) {
        d[i] = INF;
        parent[i] = -1;
        status[i] = NOT_VISITED;
    }
    d[0] = 0;

    int u, min_cost;
    while (1) {
        u = -1;
        min_cost = INF;
        for (int i = 0; i < n; i++) {
            if (min_cost > d[i] && status[i] != COMPLETE) {
                u = i;
                min_cost = d[i];
            }
        }
        if (u == -1) break;
        status[u] = COMPLETE;
        for (int i = 0; i < n; i++) {
            if (status[i] == COMPLETE || G[u][i] == INF) continue;
            if (d[i] > G[u][i]) {
                d[i] = G[u][i];
                parent[i] = u;
                status[i] = VISITED;
            }
        }
    }
    
    int sum = 0;
    for (int i = 0; i < n; i++) {
        if (parent[i] != -1) sum += G[i][parent[i]];
    }

    return sum;
}

int main() {
    cin >> n;

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

    cout << prim() << endl;

    return 0;
}

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

const int N = 100;
int n;
int A[N][N];
priority_queue< pair<int, int> > Q;

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

	int mcost = -INT_MAX;

	for (int i=0; i<n; i++)
	{
		bool visit[N] = {0};

		Q.push(pair<int, int>(0,i));

		int cost = 0;

		while (Q.size())
		{
			pair<int, int> q = Q.top();
			Q.pop();
			int k = q.second;
			if (visit[k]) continue;
			cost += q.first;
			visit[k]=true;
			for(int j=0;j<n;j++)
			{
				int c = A[k][j];
				if (c <= 0) continue;
				if (visit[j]) continue;
				Q.push(pair<int, int>(-c,j));
			}
		}

		if (mcost < cost) mcost = cost;
	}

	cout << -mcost << endl;
		
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i = 0; i < (n) ; i++)
constexpr auto INF = 2147483647;
typedef long long ll;
static const int MAX = 100;
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int n, Adjacency_Matrix[MAX][MAX];

int prim(){
  int u, minv;
  int d[MAX], p[MAX], color[MAX];
  // init
  for(int i = 0;i < n; i++){
    d[i] = INF;
    p[i]= -1;
    color[i] = WHITE;
  }

  d[0] = 0;
  while(1){
    minv = INF;
    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 && Adjacency_Matrix[u][v] != INF){
        if(d[v] > Adjacency_Matrix[u][v]){
          d[v] = Adjacency_Matrix[u][v];
          p[v] = u;
          color[v] = GRAY;
        }
      }
    }
  }
    int sum = 0;
    for(int i = 0;i<n; i++){
      if(p[i] != -1) sum += Adjacency_Matrix[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;
      Adjacency_Matrix[i][j] = (e== -1) ? INF : e;
    }
  }

  cout << prim() << endl;

  return 0;
}

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

bool self(vector<vector<int> >& G, int s, int t, vector<pair<int, int> >& stock_idx, vector<int>& searched){
    if (searched[s] == 1) return false;
    searched[s] = 1;
    if (G[s][t] != -1 && stock_idx.size() > 1) {
        stock_idx.push_back(make_pair(s, t));
        return true;
    }
    for (int i = 0; i < G[s].size(); i++) {
        if (G[s][i] != -1) {
            stock_idx.push_back(make_pair(s, i));
            if (self(G, i, t, stock_idx, searched)) return true;
            stock_idx.pop_back();
        }
    }
    return false;
}

bool DFS(vector<vector<int> >& G, int s, int t, vector<pair<int, int> >& stock_idx){
    vector<int> searched(G.size(), 0);
    return self(G, s, t, stock_idx, searched);
}

void cut(vector<vector<int> >& G, vector<pair<int, int> >& stock_idx){
    pair<int, int> max_idx = stock_idx[0];
    for (int i = 0; i < stock_idx.size(); i++) {
        if (G[stock_idx[i].first][stock_idx[i].second] > G[max_idx.first][max_idx.second]) {
            max_idx = stock_idx[i];
        }
    }
    G[max_idx.first ][max_idx.second] = -1;
    G[max_idx.second][max_idx.first ] = -1;
    stock_idx.clear();
}

int main(){
    int n;
    cin >> n;
    vector<vector<int> > G(n, vector<int>(n));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> G[i][j];
        }
    }
    for (int i = 0; i < n; i++) {
        vector<pair<int, int> > stock_idx;
        while (DFS(G, i, i, stock_idx)) cut(G, stock_idx);
    }
    int sum = 0;
    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            if (G[i][j] != -1) sum += G[i][j];
        }
    }
    cout << sum << endl;

    return 0;
}