Go: package main

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

// Define disjoint-set forests

type vertexNo int

type vertex struct {
	number vertexNo
	rank int
	parent *vertex
}

func makeSet(number vertexNo) vertex {
	return vertex {
		number: number,
		rank: 0,
		parent: nil,
	}
}

func union(x, y *vertex) *vertex {
	return link(findSet(x), findSet(y))
}

func link(x, y *vertex) *vertex {
	if x.rank > y.rank {
		y.parent = x
		return x
	} else {
		x.parent = y
		if x.rank == y.rank {
			y.rank += 1
		}
		return y
	}
}

func findSet(v *vertex) *vertex {
	if v.parent == nil {
		return v
	}
	v.parent = findSet(v.parent)
	return v.parent
}

// Function to calculate minimum spanning tree

type matrix [][]int

type edge struct {
	one vertexNo
	two vertexNo
	weight int
}

const(
	MAX_VERTICES = 100
)

func newEdgesFromMatrix(matrix matrix) []edge {
	edges := make([]edge, 0, MAX_VERTICES * MAX_VERTICES)

	for i := 0; i < len(matrix); i++ {
		row := matrix[i]
		for j := i; j < len(row); j++ {
			if row[j] >= 0 {
				edge := edge{one: vertexNo(i+1), two: vertexNo(j+1), weight: row[j]}
				edges = append(edges, edge)
			}
		}
	}

	return edges
}

func solve(matrix matrix) int {
	nVertices := len(matrix)

	// initialize vertices
	vertices := make([]vertex, nVertices)
	for i := 0; i < nVertices; i++ {
		vertices[i] = makeSet(vertexNo(i+1))
	}

	// prepare edges sorted in the ascending order of weight
	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	unionCount := 0
	weightSum := 0
	for unionCount < nVertices-1 {
		for i := 0; i < len(edges); i++ {
			edge := edges[i]
			v1 := &vertices[edge.one-1]
			v2 := &vertices[edge.two-1]
			rep1 := findSet(v1)
			rep2 := findSet(v2)
			if rep1.number == rep2.number {
				continue
			}
			union(rep1, rep2)
			edges = append(edges[0:i], edges[i+1:]...)
			weightSum += edge.weight
			unionCount++
			break
		}
	}

	return weightSum
}

// main

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

	n, err := nextInt(sc)
	if err != nil {
		panic(err)
	}

	matrix := parseMatrix(n, sc)

	edges := newEdgesFromMatrix(matrix)
	sort.Slice(edges, func(i, j int) bool {
		return edges[i].weight < edges[j].weight
	})

	fmt.Println(solve(matrix))
}

func parseMatrix(n int, sc *bufio.Scanner) [][]int {
	matrix := make([][]int, n)
	for i := 0; i < n; i++ {
		matrix[i] = make([]int, n)
		for j := 0; j < n; j++ {
			x, err := nextInt(sc)
			if err != nil {
				panic(err)
			}
			matrix[i][j] = x
		}
	}
	return matrix
}

func nextText(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextInt(sc *bufio.Scanner) (int, error) {
	return strconv.Atoi(nextText(sc))
}

C++: #include <iostream>
#include <string>
#include <vector>
#include <cstring>
#include <climits>
#include <algorithm>
#include <map>

using namespace std;

class UnionFind {
public:
    vector<int> parent;
    UnionFind(int n) : parent(n, -1) { }
    void unite(int x, int y) {
        x = root(x), y = root(y);
        if (x != y) {
            if (parent[y] < parent[x]) swap(x, y);
            parent[x] += parent[y];
            parent[y] = x;
        }
    }
    bool find(int x, int y) {
        return root(x) == root(y);
    }
    int root(int x) {
        return parent[x] < 0 ? x : parent[x] = root(parent[x]);
    }
};

int main() {
    int n;
    cin >> n;
    UnionFind uf(n);
    vector<pair<int,pair<int,int> > > E;
    int cost;
    for (int i=0; i<n; ++i) {
        for (int j=0; j<n; ++j) {
            cin >> cost;
            if (0 <= cost) {
                E.push_back(make_pair(cost, make_pair(i, j)));
            }
        }
    }
    sort(E.begin(), E.end());
    int res = 0;
    for (int i=0; i<(int)E.size(); ++i) {
        if ( ! uf.find(E[i].second.first, E[i].second.second)) {
            uf.unite(E[i].second.first, E[i].second.second);
            res += E[i].first;
        }
    }
    cout << res << endl;
    return 0;
}

C++: #include <stdio.h>

int main(){
	int n, G[100][100], tree[100][99] = { 0 };
	scanf("%d", &n);
	for (int i = 0; i < n; i++){
		for (int j = 0; j < n; j++){
			scanf("%d", &G[i][j]);
		}
	}

	int min0 = 2001;
	tree[0][0]++;
	for (int i = 1; i < n; i++){
		if (G[0][i]+1 && G[0][i] < min0){
			min0 = G[0][i];
			tree[0][1] = i;
		}
	}
	tree[tree[0][1]][0]++;

	for (int connected = 2; connected < n; connected++){
		int min = 2001,mink,minl;
		for (int k = 0; k < n; k++){
			if (!tree[k][0]){
				continue;
			}
			for (int l = 0; l < n; l++){
				if (!tree[l][0] && G[k][l] + 1 && G[k][l] < min){
					min = G[k][l];
					mink = k;
					minl = l;
				}
			}
		}
		tree[mink][++tree[mink][0]] = minl;
		tree[minl][++tree[minl][0]] = mink;
	}

	int sum = 0;
	for (int i = 0; i < n; i++){
		for (int j = 0; j < tree[i][0]; j++){
			sum += G[i][tree[i][j + 1]];
		}
	}

	printf("%d\n", sum >> 1);
	return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
#define INF 2000000
#define MAX 20000
int m[MAX][MAX],color[MAX],d[MAX],num;
int spaning(){
	for(int i=0;i<num;i++){
		color[i]=0;d[i]=INF;
	}
	d[0]=0;
	int sum=0;
	int min_now=INF;
	while(1){
		int v=-1;
	for(int i=0;i<num;i++){
		if(!color[i]&&(v==-1||d[v]>d[i])){
			v=i;
		}}
		if(v==-1) break;
		sum+=d[v];
		color[v]=1;
	for(int i=0;i<num;i++){
		if(!color[i]){
			d[i]=min(d[i],m[v][i]);
		}
	
	}
	}
	return sum;
}
int main(){
	int a;
	cin>>num;
	for(int i=0;i<num;i++){
		for(int j=0;j<num;j++){
			cin>>a;
			if(a==-1) m[i][j]=INF;
			else m[i][j]=a;
		}
	}
	int s=spaning(); 
	cout<<s<<endl;
}

C++: #include <iostream>
#include <queue>
#include <vector>
#include <utility>
using namespace std;
typedef pair<int,int> Info;
int main(){
        int N;
        cin >> N;
        vector <vector<int> > adjancey(N,vector<int>(N));
        priority_queue<Info, vector<Info>,greater<Info> > descending;
        for(int i=0 ; i<N ; i++ )
                for(int j=0 ; j<N ; j++ )
                        cin >> adjancey[i][j];
        Info wn;
        int now=0,counter=0;
        vector <bool> past(N,false);
        while(true){
                past[now]=true;
                for(int i=0 ; i<N ; i++ ){
                        if(past[i])
                                continue;
                        if(adjancey[now][i]==-1)
                                continue;
                        wn.first=adjancey[now][i];
                        wn.second=i;
                        descending.push(wn);
                }
                int c=0;
                for(int i=0;i<N;i++)
                        c+=past[i];
                if(c==N)break;
                wn=descending.top();descending.pop();
                now=wn.second;
                if(past[now])continue;
                counter+=wn.first;
        }
        cout << counter << endl;
        return 0;
}

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

using namespace std;

int P[110];
pair<int,int> bridge[10010];

void init(int N){
  for(int i = 0;i<N;i++){
    P[i] = i;
  }
}

int root(int a){
  if(P[a] == a){
    return a;
  }
  return(P[a] = root(P[a]));
}

bool is_same_set(int a,int b){
  return root(a) == root(b);
}

void unite(int a,int b){
  P[root(a)] = root(b);
}

int main(){
  int n,a[10010],b[10010],w,count = 0,result = 0,x,y;
  cin >>n;
  init(n);
  for(int i=0;i<n;i++){
    for(int k=0;k<n;k++){
      cin >> w;
      if(w >= 0){
        bridge[count].first = w;
        a[count] = i;
        b[count] = k;
        bridge[count].second = count;
        count ++;
      }
    }
  }
  sort(bridge,bridge+count);
  for(int i=0;i<count;i++){
    x = a[bridge[i].second];
    y = b[bridge[i].second];
    if(!is_same_set(x,y)){
      unite(x,y);
      result += bridge[i].first;
      //cout << x <<" " << y << " " << bridge[i].first << endl;
    }
  }
  cout << result << endl;
}