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 <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); i++)
using namespace std;
using ll = long long;

constexpr int LEN = 105;
int a[LEN][LEN];

int prim(int n){
	bool check[n];
	int p[n], d[n];
	memset(check, 0, n*sizeof(bool));
	memset(p, -1, n*sizeof(int));
	memset(d, 1, n*sizeof(int));
	rep(i, n) p[i] = INT_MAX;
	d[0] = 0;
	p[0] = -1;

	while(true){
		int min_cost = INT_MAX;
		int now_v;
		rep(i, n){
			if(!check[i] && d[i] < min_cost){
				min_cost = d[i];
				now_v = i;
			}
		}
		if(min_cost == INT_MAX) break;

		check[now_v] = true;

		rep(v, n){
			if(!check[v] && (a[now_v][v] > -1) && (a[now_v][v] < d[v])){
				d[v] = a[now_v][v];
				p[v] = now_v;
			}
		}
	}

	int sum = 0;
	rep(i, n) sum += d[i];

	return sum;
}

int main(){
	int n; cin >> n;
	rep(i, n)rep(j, n) {
		int w; cin >> w;
		a[i][j] = w;
		a[j][i] = w;
	}

	cout << prim(n) << endl;

	return 0;
}

C++: //Minimum Spannig Tree
#include <iostream>
#include <climits>

using namespace std;

static const int N = 100;
static const int WHITE = 0;
static const int BLACK = 1;
int n, A[N][N], colors[N], d[N], p[N];

int prim() {
    int l = 0, mincost, u;
    for(int i = 0; i < N; i++) {
        colors[i] = WHITE;
        d[i] = INT_MAX;
    }
    d[0] = 0;
    p[0] = -1;
    while(1) {
        mincost = INT_MAX;
        for(int i = 0; i < n; i++) {
            if(colors[i] == WHITE && d[i] < mincost) {
                mincost = d[i];
                u = i;
            }
        }
        if(mincost == INT_MAX) break;
        colors[u] = BLACK;
        l += mincost;
        for(int v = 0; v < n; v++) {
            if(colors[v] == WHITE && A[u][v] != -1) {
                if(A[u][v] < d[v]) {
                    d[v] = A[u][v];
                    p[v] = u;
                }
            }
        }
    }
    return l;
}

int main() {
    int a;
    cin >> n;
    for(int i = 0; i < N; i++) {
        for(int j = 0; j < N; j++) A[i][j] = -1;
    }
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++){
            cin >> a;
            A[i][j] = a;
        }
    }
    cout << prim() << endl;
}

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;

int n, M[MAX][MAX];

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

   d[0] = 0;

   while ( 1 ) {
      min = INFTY;
      u = -1;

      for ( int i = 0; i < n; i++ ) {
         if ( min > d[i] && color[i] != BLACK ) {
            a = i;
            min = d[i];
         }
      }

      if ( a == -1 ) break;
      color[a] = BLACK;
      for ( int v = 0; v < n; v++ ) {
         if ( color[v] != BLACK && M[a][v] != INFTY ) {
            if ( d[v] > M[a][v] ) {
               d[v] = M[a][v];
               color[v] = GRAY;
            }
         }
      }
   }

   int sum = 0;
   for ( int i = 0; i < n; i++ ) {
      if ( p[i] != -1 ) sum = sum + M[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;
         M[i][j] = (e == -1) ? INFTY : e;
      }
   }

   cout << prim() << endl;

   return 0;
}

C++: #include <iostream>
using namespace std;
#define N 100
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INFTY 10000

int n, M[N][N];


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

  while(true){
    mincost = INFTY;
    u = -1;
    //TとV-Tをつなぐ辺の中で最小のものを探す
    for(int i = 0 ; i < n ; i++){
      if(color[i] != BLACK && d[i] < mincost ){
        mincost = d[i];
        u = i;
      }
    }
    if(u == -1){
      break;
    }
    color[u] = BLACK;

    //Tの中の各頂点からのV-Tの頂点への最短辺の長さをd[v]に入れる
    for(int v = 0 ; v < n ; v++){
      if(color[v] != BLACK && M[u][v] != INFTY){
        if(M[u][v] < d[v]){
          d[v] = M[u][v];
          p[v] = u;
          color[v] = GRAY;
        }
      }
    }

  }
  int sum = 0;
  for(int i = 0 ; i < n ; i ++){
    if(p[i] != -1){
      sum += M[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;
      M[i][j] = (e == -1) ? INFTY: e;
    }
  }
  //int sum = prim();
  cout << prim() << "\n";
  return 0;

}

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

const int I_MAX = 0xfffffff;
const int MAX = 100;


int main() {
	int n;
	int graph[MAX][MAX];
	bool table[MAX] = { false };
	int sum = 0;

	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int temp;
			cin >> temp;
			if (temp == -1)temp = I_MAX;
			graph[i][j] = temp;
		}
	}

	table[0] = true;

	for (int i = 0; i < n - 1; i++) {
		int cost = I_MAX;
		int m;

		for (int j = 0; j < n; j++) {
			if (table[j] == false)continue;

			for (int k = 0; k < n; k++) {
				if (graph[j][k] < cost && table[k] == false) {
					cost = graph[j][k];
					m = k;
				}
			}
		}

		sum += cost;
		table[m] = true;
	}

	cout << sum << endl;

	return 0;
}