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 <queue>
#include <climits>
using namespace std;

const int N = 100;
int n;
int A[N][N];
bool visit[N] = {0};
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];
		}
	}

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

	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));
		}
	}

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

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, G[MAX][MAX];

int prim() {
  int u, minv;
  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 ) {
    minv = INFTY;
    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 && M[u][v] != INFTY ) {
        if( d[v] > M[u][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;
    }
  }

  cout << prim() << endl;

  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define N_MAX 100

int M[N_MAX][N_MAX];

int main(){

  int n;
  scanf("%d", &n);

  for(int i=0; i<n*n; i++){
    scanf("%d", &M[i/n][i%n]);
  }

  /*
   * Find Mininum Spanning Tree using
   * Prim's Algorithm
  */
  vector<bool> is_belong_to_mst(n, false);
  is_belong_to_mst.at(0) = true;
  int total_cost = 0;
  for(int i=1; i<n; i++){
    // get t and adj
    vector<int> t;
    vector<int> adj;
    for(int i=0; i<n; i++){
      if(is_belong_to_mst.at(i)) t.push_back(i);
      else adj.push_back(i);
    }

    int min_cost = INT_MAX;
    int next_t = 0;
    for(int i=0; i<t.size(); i++){
      for(int j=0; j<adj.size(); j++){
        if(M[t.at(i)][adj.at(j)] != -1 && M[t.at(i)][adj.at(j)] < min_cost){
          min_cost = M[t.at(i)][adj.at(j)];
          next_t = adj.at(j);
        }
      }
    }

    is_belong_to_mst.at(next_t) = true;
    total_cost += min_cost;
  }

  printf("%d\n", total_cost);

  return 0;
}

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

static const int MAX_NUM  = 101;
static const int NO_VISIT  = 0;
static const int NOW_VISIT = 1;
static const int END_VISIT = 2;

void MPT(int *pElem, int num)
{
    int i;
    int mincost;
    int target;
    int parent[MAX_NUM];
    int cost[MAX_NUM];
    int state[MAX_NUM] = {0};
    int *tmp;
    int total = 0;

    for (i = 0; i < num; i++) {
        parent[i] = -1;
        cost[i]   = 0x7FFFFFFF;
    }

    cost[0] = 0;

    for (;;) {
        mincost = 0x7FFFFFFF;
        for (i = 0; i < num; i++) {
            if ((state[i] != END_VISIT) && (mincost > cost[i])) {
                target  = i;
                mincost = cost[i];
            }
        }
        if (mincost == 0x7FFFFFFF) {
            break;
        }

        tmp = pElem + target * MAX_NUM;
        for (i = 0; i < num; i++) {
            if (*(tmp + i) < cost[i]) {
                cost[i]   = *(tmp + i);
                parent[i] = target;
                state[i]  = NOW_VISIT;
            }
        }
        state[target] = END_VISIT;
        total += cost[target];
    }

    printf("%d\n", total);

    return;
}

int main(void)
{
    int i, j;
    int num;
    int tmp;
    int elem[MAX_NUM][MAX_NUM];

    scanf("%d", &num);
    for (i = 0; i < num; i++) {
        for (j = 0; j < num; j++) {
            scanf("%d", &tmp);
            elem[i][j] = (tmp != -1) ? tmp : 0x7FFFFFFF;
        }
    }

    MPT(&elem[0][0], num);

    return 0;
}