Go: package main

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

// I/O
type Scanner struct {
	sc *bufio.Scanner
}

func NewScanner() *Scanner {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)
	sc.Buffer(make([]byte, 1024), int(1e+9))
	return &Scanner{sc}
}

func (s *Scanner) nextStr() string {
	s.sc.Scan()
	return s.sc.Text()
}

func (s *Scanner) nextInt() int {
	i, e := strconv.Atoi(s.nextStr())
	if e != nil {
		panic(e)
	}
	return i
}

func (s *Scanner) nextFloat() float64 {
	f, e := strconv.ParseFloat(s.nextStr(), 64)
	if e != nil {
		panic(e)
	}
	return f
}

func (s *Scanner) nextRuneSlice() []rune {
	return []rune(s.nextStr())
}

func (s *Scanner) nextIntSlice(n int) []int {
	res := make([]int, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextInt()
	}
	return res
}

func (s *Scanner) nextFloatSlice(n int) []float64 {
	res := make([]float64, n)
	for i := 0; i < n; i++ {
		res[i] = s.nextFloat()
	}
	return res
}

// Arithmetic
func max(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m < i {
			m = i
		}
	}
	return m
}

func min(nums ...int) int {
	m := nums[0]
	for _, i := range nums {
		if m > i {
			m = i
		}
	}
	return m
}

func abs(x int) int {
	if x > 0 {
		return x
	}
	return -x
}

func pow(x, y int) int {
	res := 1
	for i := 0; i < y; i++ {
		res *= x
	}
	return res
}

func ceil(a, b int) int {
	if a%b == 0 {
		return a / b
	} else {
		return a/b + 1
	}
}

// Sort
type RuneSlice []rune

func (a RuneSlice) Len() int           { return len(a) }
func (a RuneSlice) Less(i, j int) bool { return a[i] < a[j] }
func (a RuneSlice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

const INF = 1 << 60

// Main
func main() {
	sc := NewScanner()
	wtr := bufio.NewWriter(os.Stdout)
	N := sc.nextInt()
	G := make([][]int, N)
	for i := 0; i < N; i++ {
		G[i] = make([]int, N)
		for j := 0; j < N; j++ {
			G[i][j] = sc.nextInt()
		}
	}
	d := make([]int, N)
	for i := 0; i < N; i++ {
		d[i] = INF
	}
	seen := make([]bool, N)
	d[0] = 0
	ans := 0
	for {
		cur := 0
		minCost := INF
		for i := 0; i < N; i++ {
			if !seen[i] && d[i] < minCost {
				minCost = d[i]
				cur = i
			}
		}
		if minCost == INF {
			break
		}
		seen[cur] = true
		ans += d[cur]
		for i := 0; i < N; i++ {
			cost := G[cur][i]
			if cost != -1 && cost < d[i] {
				d[i] = cost
			}
		}
	}

	fmt.Fprintln(wtr, ans)
	wtr.Flush()
}

C++: #include <iostream>

using namespace std;

#define MAX 100
#define INFTY 9999999 
#define WHITE 0
#define GRAY 1
#define BLACK 2

int M[MAX][MAX];
int color[MAX];
int d[MAX];
int p[MAX];
int n;

int prim()
{
	int mincost;
	int u;

	for (int i = 0; i < MAX; i++) {
		d[i] = INFTY;
		p[i] = -1;
	}

	d[0] = 0;
	p[0] = -1;

	while (true) {
		mincost = INFTY;

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


		if (mincost == INFTY) {
			break;
		}

		color[u] = BLACK;

		for (int i = 0; i < n; i++) {
			if (color[i] != BLACK&&M[u][i] != -1) {
				if (M[u][i] < d[i]) {
					d[i] = M[u][i];
					p[i] = u;
					color[i] = GRAY;
				}
			}
		}
	}


	int sum = 0;

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

	return sum;

}



int main(void)
{



	cin >> n;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> M[i][j];
		}
	}

	cout << prim() << endl;

	return 0;
}

C++: #include <iostream>
#include <climits>
#include <queue>

using namespace std;

using pii = pair<int, int>;

struct Graph{
  int v_size;
  vector<vector<pii>> adj;
  
  Graph(const int v_size):v_size(v_size){
    this->adj.resize(v_size);
  }
  
  void add_edge(const int s, const int t, const int w){
    this->adj[s].emplace_back(pii(t, w));
  }
};

int mst(const Graph& g){
  constexpr int INF{INT_MAX};
  
  vector<int> d(g.v_size, INF);
  priority_queue<pii, vector<pii>, greater<pii>> pq;

  d[0] = 0;
  pq.push(pii(0, 0));

  int ans {0};
  
  while(!pq.empty()){
    auto cost {pq.top().first};
    auto v {pq.top().second};
    pq.pop();

    if(d[v] < cost) continue;

    ans += cost;
    d[v] = -INF;

    for(int i = 0; i < g.adj[v].size(); ++i){
      auto to {g.adj[v][i].first};
      auto next_cost {g.adj[v][i].second};

      if(d[to] > next_cost){
        d[to] = next_cost;
        pq.push(pii(next_cost, to));
      }
    }
  }

  return ans;
}

int main()
{
  int n;
  cin >> n;
  
  Graph g(n);

  int x;
  for(int i = 0; i < n; ++i){
    for(int j = 0; j < n; ++j){
      cin >> x;
      if(x != -1){
        g.add_edge(i, j, x);
      }
    }
  }

  cout << mst(g) << endl;
}

C++: #include <iostream>
#include <vector>
#include <queue>
#define to first
#define cost second
const int inf=1e9+7;
using namespace std;
int main(){

  int n,tmp,r=0,flag[100]={},v=0;
  cin>>n;
  vector <pair<int,int> > gl[n];
  priority_queue <pair<int,int> ,vector<pair<int,int> >, greater<pair<int,int> > >q;
  //for(int i=1;i<n;i++) mincost[i]=inf;                                                                                                                                                       

  for(int i=0;i<n;i++) for(int j=0;j<n&&cin>>tmp;j++) if(tmp!=-1) gl[i].push_back(make_pair(j,tmp));
  int now=0;
  for(int j=0;j<n-1;j++){
    for(int i=0;i<gl[now].size();i++) if(!flag[gl[now][i].to]) q.push(make_pair(gl[now][i].cost,gl[now][i].to));
    flag[now]=1;
    //for(;flag[q.top().second];) q.pop();                                                                                                                                                     
    //if(q.empty()) break;                                                                                                                                                                     
    r+=q.top().first;
    now=q.top().second;
    q.pop();
  }
  cout<<r<<endl;
  return 0;

}

C++: //ALDS1_12A
#include <iostream>
using namespace std;

static const int MAX=100;
static const int INF=(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]=INF;
  p[i]=-1;
  color[i]=WHITE;
 }
 d[0]=0;
 while(true){
  minv=INF;
  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]!=INF){
    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) ? INF:e;
  }
 }
 cout<<prim()<<endl;
 return 0;
}