Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

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

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

C++: #include <iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1 << 21);
static const int NOT_VISIT = 0;
static const int VISITING = 1;
static const int VISITED = 2;
int n;
int M[MAX][MAX];
int prim()
{
    int minv, u;
    int isVisited[MAX], d[MAX], p[MAX];
    for (int i = 0; i < n; i++) {
	isVisited[i] = NOT_VISIT;
	d[i] = INFTY;
	p[i] = -1;
    }
    d[0] = 0;
    while (1) {
	minv = INFTY;
	u = -1;
	for (int i = 0; i < n; i++) {
	    if (minv > d[i] && isVisited[i] != VISITED) {
		u = i;
		minv = d[i];
	    }
	}
	if (u == -1) {
	    break;
	}

	isVisited[u] = VISITED;
	for (int j = 0; j < n; j++) {
	    if (isVisited[j] != VISITED && M[u][j] != INFTY) {
		if (d[j] > M[u][j]) {
		    d[j] = M[u][j];
		    p[j] = u;
		    isVisited[j] = VISITING;
		}
	    }
	}
    }
    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;
}

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 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;
}