Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

type ElementKey int
type Node struct {
	key    ElementKey
	parent *Node
	rank   int
}

func newNode(key ElementKey) *Node {
	node := Node{}
	node.key = key
	node.parent = &node
	node.rank = 0

	return &node
}

func union(x, y *Node) {
	xSet := findSet(x)
	ySet := findSet(y)
	link(xSet, ySet)
}

func link(x, y *Node) {
	if x.rank > y.rank {
		y.parent = x
	} else {
		x.parent = y

		if x.rank == y.rank {
			y.rank++
		}
	}
}

func findSet(x *Node) *Node {
	if x != x.parent {
		x.parent = findSet(x.parent)
	}
	return x.parent
}

func newDisjointSets(nSets int) *DisjointSets {
	sets := DisjointSets{}
	sets.keyToNode = map[ElementKey]*Node{}
	for i := 0; i < nSets; i++ {
		key := ElementKey(i)
		sets.keyToNode[key] = newNode(key)
	}
	return &sets
}

type DisjointSets struct {
	keyToNode map[ElementKey]*Node
}

func (sets *DisjointSets) union(x, y ElementKey) {
	xNode := sets.keyToNode[x]
	yNode := sets.keyToNode[y]
	union(xNode, yNode)
}

func (sets DisjointSets) findSet(x ElementKey) *Node {
	xNode := sets.keyToNode[x]
	return findSet(xNode)
}

type Edge struct {
	i, j   int
	weight int
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	sets := newDisjointSets(n)
	edges := []Edge{}
	a := make([][]int, n)
	for i := 0; i < n; i++ {
		a[i] = make([]int, n)
		for j := 0; j < n; j++ {
			a[i][j] = nextInt()
			if a[i][j] >= 0 {
				e := Edge{
					i:      i,
					j:      j,
					weight: a[i][j],
				}
				edges = append(edges, e)
			}
		}
	}
	sort.Slice(edges, func(i, j int) bool { return edges[i].weight < edges[j].weight })
	totalWeight := 0
	for _, edge := range edges {
		i := ElementKey(edge.i)
		j := ElementKey(edge.j)
		if sets.findSet(i) != sets.findSet(j) {
			totalWeight += edge.weight
			sets.union(i, j)
		}
	}
	fmt.Println(totalWeight)
}

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 = 0; 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;
}

C++: #include<bits/stdc++.h>
using namespace std;
const int MAXN = 100+7;
const int INF = 2e3+7;
int m[MAXN][MAXN];
int sum;
set<int> notin;
set<int> isin;
bool visit[MAXN];
void printset(set<int> r)
{

    for(set<int>::iterator it = r.begin(); it != r.end(); it++)
    {
        printf("%d,", *it);
    }
    printf("\n");
}
void prim(int root)
{
    isin.insert(root);
    notin.erase(root);
    visit[root] = true;
    while(!notin.empty())
    {
        int u;
        int min_e = INF;
        for(set<int>::iterator it = isin.begin(); it!=isin.end(); it++)
        {
            int r = *it;
            int i;
            for(set<int>::iterator it2 = notin.begin(); it2!=notin.end(); it2++)
            {
                int h = *it2;
                if(m[h][r]<min_e && m[h][r]!=-1 && visit[h] == false)
                {
                    min_e = m[h][r];
                    u = h;
                }

            }
        }
        isin.insert(u);
        notin.erase(u);
        visit[u] = true;
        sum+=min_e;
    }
}
int main()
{
//    freopen("../in.txt", "r", stdin);
    memset(visit, false, sizeof(visit));
    int n;
    scanf("%d", &n);
    int i, j;
    for(i = 0; i < n; i++)
    {
        for(j = 0; j < n; j++)
        {
            scanf("%d", &m[i][j]);
        }
        notin.insert(i);

    }
    sum = 0;
    prim(0);
    printf("%d\n", sum);
    return 0;
}

C++: #include <iostream>

using namespace std;

static const int N = 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[N][N];

int prim()
{
	int d[N], p[N], color[N];

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

	d[0] = 0;

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

		if (u == -1) break;
		color[u] = BLACK;

		for (int v = 0; v < n; ++v)
		{
			if (m[u][v] != INFTY && color[v] != BLACK && m[u][v] < d[v])
			{
				d[v] = m[u][v];
				p[v] = u;
				color[v] = GRAY;
			}
		}
	}

	int s = 0;
	for (int i = 0; i < n; ++i)
	{
		if (p[i] != -1) s += m[p[i]][i];
	}

	return s;
}

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 <iostream>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <string>
#include <cstring>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <stack>
#include <queue>
#include <algorithm>

using namespace std;

// ---------------------
// repetition
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

// debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

// ---------------------
#define INF 922337203685477580
typedef long long ll;

int main() {
  int n;
  cin >> n;

  int G[n][n];
  int visited[n];
  int d[n];
  int p[n];
  REP(y, n) {
    REP(x, n) {
      int cost;
      cin >> cost;

      if (cost == -1) {
        G[y][x] = 1 << 15;
      } else {
        G[y][x] = cost;
      }
    }
    visited[y] = 0;
    d[y] = 1 << 15;
    p[y] = -1;
  }

  d[0] = 0;

  REP(_, n) {
    int mincost = 1 << 15;
    int minv = -1;
    REP(v, n) {
      if (!visited[v] && d[v] < mincost) {
        minv = v;
        mincost = d[v];
      }
    }
    visited[minv] = 1;
    REP(to, n) {
      if (!visited[to] && G[minv][to] < (1 << 15) && G[minv][to] < d[to]) {
        d[to] = G[minv][to];
        p[to] = minv;
      }
    }
  }

  ll sum = 0;
  REP(i, n) {
    if (p[i] != -1) {
      sum += G[i][p[i]];
    }
  }

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

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

struct Edge{
  int weight;
  int from;
  int to;
  Edge(int w,int f,int t):weight(w),from(f),to(t){}
};

const int inf = 1<<28;

bool operator<(Edge e1,Edge e2){
  return (e1.weight < e2.weight);
}

int nlist[110];

int parent(int i){
  if(nlist[i] == i) return i;
  else return (nlist[i] = parent(nlist[i]));
}

int main(){
  int n;
  cin>>n;
  vector<Edge> Elist;
  for(int i=0;i<n;i++) nlist[i]=i;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      int temp;
      cin>>temp;
      if(temp != -1){
	Elist.push_back(Edge(temp,i,j));
      }
    }
  }
  sort(Elist.begin(),Elist.end());
  int ans = 0;
  for(int i=0;i<Elist.size();i++){
    Edge e = Elist[i];
    int fp = parent(e.from);
    int tp = parent(e.to);
    if(fp != tp){
      ans += e.weight;
      nlist[fp] = tp;
    }
  }
  cout<<ans<<endl;
  return 0;
}