Go: package main

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

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX   = 100
	INFTY = (1 << 21)
	WHITE = 0
	GRAY  = 1
	BLACK = 2
)

//V: グラフの頂点全体の集合
//T: MSTに属する頂点の集合
var (
	n     int
	M     [MAX][MAX]int //重みを記録する隣接行列
	color [MAX]int
	p     [MAX]int //MSTにおける頂点の親を記録
	d     [MAX]int //Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを記録
)

func prim() int {
	var u, minv int
	//初期化
	for i := 0; i < n; i++ {
		d[i] = INFTY
		p[i] = -1
		color[i] = WHITE
	}

	d[0] = 0

	for {
		//頂点uを決めていく
		//つまり、Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを決める
		minv = INFTY
		u = -1
		for i := 0; i < n; i++ {
			//未訪問かつ、辺の重みが最小となるuを選ぶ
			if minv > d[i] && color[i] != BLACK {
				u = i
				minv = d[i]
			}
		}

		if u == -1 {
			break
		}

		color[u] = BLACK
		for v := 0; v < n; v++ {
			//未訪問かつ、辺が存在するとき
			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
				}
			}
		}
	}

	sum := 0
	for i := 0; i < n; i++ {
		if p[i] != -1 {
			sum += M[i][p[i]]
		}
	}
	return sum
}

func main() {
	sc.Split(bufio.ScanWords)
	n = nextInt()

	for i := 0; i < n; i++ {

		for j := 0; j < n; j++ {
			tmp := nextInt()
			if tmp == -1 {
				tmp = INFTY
			}
			M[i][j] = tmp
		}

	}

	fmt.Println(prim())

}

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;

struct Node{
  int color, dist, parent;
};

int n, M[MAX][MAX];
Node node[MAX];

void Printnodes(){
  string col[3] = {"WHITE", "GRAY ", "BLACK"};
  for(int i = 0; i < n; i++){
    cout << "nodeID : " << i ;
    cout << " color : " << col[node[i].color];
    cout << " parent : " << node[i].parent;
    cout << " dist : " << node[i].dist << endl;
  }
  cout << endl;
}

int main(){
  cin >> n;

  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> M[i][j];
    }
    node[i].color = WHITE;
    node[i].dist = INFTY;
    node[i].parent = -1;
  }

  int p = 0;
  node[p].color = BLACK;
  node[p].dist = 0;

  while(true){
    //Printnodes();

    for(int i = 0; i < n; i++){
      if(M[p][i] > 0 && node[i].color != BLACK){
        node[i].dist = M[p][i];
        node[i].parent = p;
        node[i].color = GRAY;
      }
    }

    int min_d = INFTY;
    p = -1;
    for(int i = 0; i < n; i++){
      if(node[i].dist < min_d && node[i].color != BLACK){
        min_d = node[i].dist;
        p = i;
      }
    }

    if(p == -1)
      break;

    node[p].color = BLACK;
    //cout << "node " << p << " turns to BLACK!" << endl;
  }

  int sum = 0;

  for(int i = 0; i < n; i++){
    if(node[i].parent >= 0)
      sum += M[i][node[i].parent];
  }
  cout << sum << endl;
  return 0;
}

C++: #include<iostream>
#include<vector>

struct Edge {
	int row, column, weight;
};

void divide_graph(bool[], int);

int n;
Edge edges[99]{};

int main()
{
	int in_tmp, min{}, matrix[100][100]{};

	std::cin >> n;
	for (int i = 0; i < n; ++i)
		for (int j = 0; j < n; ++j)
		{
			std::cin >> in_tmp;
			matrix[i][j] = in_tmp;
		}

	int rest = n - 1, pre_size = 0;
	std::vector<int> queue{ 0 };
	bool visited[100]{ true };
	for (int i = 1; rest; ++i)
	{
		int now_size = queue.size();
		for (int j = pre_size; j < now_size; ++j)
			for (int k = 0; k < n; ++k)
			{
				int tmp = matrix[queue[j]][k];
				if (tmp != -1 && !visited[k])
				{
					visited[k] = true;
					rest--;
					edges[queue.size() - 1] = { queue[j], k , tmp};
					queue.push_back(k);
				}
			}
		pre_size = now_size;
	}
	for (int i = 0; i < n - 1; ++i)
	{
		bool conne_row[100]{};
		divide_graph(conne_row, i);

		for (int j = 0; j < n; ++j)
		{
			if (!conne_row[j]) continue;
			for (int k = 0; k < n; ++k)
			{
				if (conne_row[k]) continue;
				if (matrix[j][k] == -1 || matrix[j][k] >= edges[i].weight) continue;

				edges[i] = { j, k, matrix[j][k] };
			}
		}
	}

	for (int i = 0; i < n - 1; ++i)
		min += edges[i].weight;

	std::cout << min << std::endl;
	
	return 0;
}

void divide_graph(bool conne_row[], int max_edge)
{
	conne_row[edges[max_edge].row] = true;

	std::vector<int> queue = { edges[max_edge].row };
	int pre_size = 0;

	bool visit_edge[100]{};
	visit_edge[max_edge] = true;

	while (pre_size != queue.size())
	{
		int now_size = queue.size();
		for (int j = pre_size; j < now_size; ++j)
		{
			for (int k = 0; k < n - 1; ++k)
			{
				if (visit_edge[k]) continue;
				if (edges[k].row == queue[j])
				{
					visit_edge[k] = true;
					conne_row[edges[k].column] = true;
					queue.push_back(edges[k].column);
				}
				else if (edges[k].column == queue[j])
				{
					visit_edge[k] = true;
					conne_row[edges[k].row] = true;
					queue.push_back(edges[k].row);
				}
			}
		}
		pre_size = now_size;
	}
	return;
}

C++: #include<iostream>
#include<sstream>
#include<fstream>
#include<string>
#include<vector>
#include<deque>
#include<queue>
#include<stack>
#include<set>
#include<map>
#include<algorithm>
#include<functional>
#include<utility>
#include<bitset>
#include<cmath>
#include<cstdlib>
#include<ctime>
#include<cstdio>

using namespace std;

#define REP(i,n) for(int i=0;i<int(n);i++)
#define foreach(c,itr) for(__typeof((c).begin()) itr=(c).begin();itr!=(c).end();itr++)
typedef long long ll;
typedef pair<int,int> P;

int V;
int cost[110][110];
int mincost[110];
bool vis[110];
const int INF=1e9;

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

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

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

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

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

int main(void){
	          int i,j;

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

	          cout << prim() << endl;

	          return 0;
}

C++: #include<iostream>
#include<vector>
#include<algorithm>

int color(std::vector<std::vector<int> > v) {
	std::vector<int> color(v.size(), 0);
	int count = 0, color_count = 1;
	for (int i = 1; i <= 2000; i++) {
		for (size_t j = 0; j < v.size(); j++) {
			for (size_t k = j + 1; k < v.size(); k++) {
				if (v[j][k] == i && ((color[k] == 0 || color[j] == 0) || (color[k] != color[j]))) {
					if (color[k] == 0) {
						if (color[j] != 0) {
							color[k] = color[j];
						} else {
							color[k] = color[j] = color_count;
							color_count++;
						}
					} else {
						if (color[j] == 0) {
							color[j] = color[k];
						} else {
							int num = color[j];
							std::replace(color.begin(), color.end(), num, color[k]);
						}
					}
					count += i;
				}
			}
		}
	}
	return count;
}

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::cout << color(v) << std::endl;

	return 0;
}