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>
#include <cstdio>
using namespace std;
static const int  N = 100;
static const int  INFTY = (1<<21);
int M[N][N], color[N];
int n, d[N], p[N];
int ans = 0;

int prim()
{
    for (int i = 0; i < n; i++)
    {
        color[i] = -1;
        d[i] = INFTY;
        p[i] = -1;
    } 
    d[0] = 0;
    int u = -1;
    while (true)
    { 
        int mincost = INFTY;
        u = -1;
        for (int i = 0; i < n; i++)
        {
            if (color[i] != 2 && d[i] < mincost)
            { 
                mincost = d[i];
                u = i;
            }  
        } 

        if (mincost == INFTY) break;
        color[u] = 2;
        for (int i = 0; i < n; i++)
        {
            if (color[i] != 2 && M[u][i] != INFTY)
            { 
                if (M[u][i] < d[i])
                { 
                    d[i] = M[u][i];
                    p[i] = u;
                    color[i] = 1;
                }  
            }  
        } 
    }

    for (int i = 0; i < n; i++)
    {
        if (color[i] == 2 && p[i] != -1) ans += M[i][p[i]];

    } 
    return ans;
}

int main()
{
    cin>>n;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            int a;
            cin>>a;
            if(a != -1) M[i][j] = a;
            else M[i][j] = INFTY;
        }  
    } 
    prim();
    cout<<ans<<endl;    
    return 0;
}

C++: #include<stdio.h>

static const int MAX = 500;
static const int INFTY = (1<<21);

main(){
  int n, i, j, e, sum,M[MAX][MAX]={0};
  int u,minV,INT_MAX,A[MAX]={INFTY},key[MAX]={INFTY};
  /*

    your code


   */

  scanf("%d", &n);
  
  for ( i = 0; i< n; i++ ){
    for ( j = 0; j < n; j++ ){
      scanf("%d", &e);
      M[i][j] = (e==-1)?INFTY:e;
    }
  }
  
  
  while(){
    minV = 
      for(i=1;i<=n;i++){
        if((i < minV) && 

  






















  sum = 0;

  for ( i = 0; i < n; i++ ){
    if ( p[i] != -1 ) sum += M[i][p[]];
  }

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

  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;
typedef long long ll;

static const int INF = 1e9;
static const int MAX = 100;

int n;
struct edge{int to, cost;};
typedef pair<int, int> P;

int mincost[MAX];
bool used[MAX];
vector< vector<edge> > A(MAX);

int prim(){
    int to, cost, res = 0;
    priority_queue<P, vector<P>, greater<P>> que;
    fill(mincost, mincost + n, INF);
    fill(used, used + n, false);
    mincost[0] = 0;
    que.push(P(0, 0));

    while(!que.empty()){
        P p = que.top(); que.pop();
        if (used[p.second]) continue;
        used[p.second] = true;

        for (int i = 0; i < A[p.second].size(); i++){
            to = A[p.second][i].to;
            cost = A[p.second][i].cost;
            if (used[to]) continue;
            if (mincost[to] > cost){
                mincost[to] = cost;
                que.push(P(mincost[to], to));
            }
        }
    }
    for (int i = 0; i < n; i++) res += mincost[i];
    return res;
}

int main(){
    cin >> n;
    edge x;
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            scanf("%d", &x.cost);
            x.to = j;
            if (x.cost != -1) A[i].push_back(x);
        }
    }
    cout << prim() << endl;
    return 0;
}

C++: #include <iostream>
#include <cstdlib>
#include <string>
#include <typeinfo>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
using namespace std;
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;
static const int INFTY = (1<<21);
static const int MAX =100;

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;
}

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

typedef long long ll;

struct Edge {
    ll s,t;
    ll w;
    bool operator < (const Edge& tgt) const {
	return w > tgt.w;
    }
    void dump(){
	cout << s << " --> " << t << " : " << w << endl; 
    }
};

ll Prim(vector<vector<Edge>>& G) {
    const ll V = G.size();
    priority_queue<Edge> edges;
    
    vector<int> used(V,0);
    edges.push( Edge{-1,0,0} );
    ll ans = 0;
    while( edges.size() ) {
	Edge e = edges.top(); edges.pop();

//	assert(used[e.s] == 1);
	if( used[e.t] == 1 ) continue;
	used[e.t] = 1;
//	e.dump();
	ans += e.w;

	for(auto& nxt : G[e.t]) {
	    if( used[nxt.t] == 1 ) continue;
	    edges.push(nxt);
	}
    }
    for(auto& e : used) assert(e == 1);

    return ans;
}


int main () {

    ll V;
    cin >> V;
    vector<vector<Edge>> G(V);

    for(int i=0; i<V; i++) {
	for(int j=0; j<V; j++) {
	    ll w; cin >> w;
	    if( w != -1 ) {
		G[i].push_back( Edge{i,j,w} );
//		G[j].push_back( Edge{j,i,w} );
//		cout << i << " <--> " << j << " : " << w << endl; 
	    }
	}
    }

    ll ans = Prim(G);
    cout << ans << endl;
        
    return 0;
}