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;

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;
}

C++: #include<bits/stdc++.h>
#define REP(i,n) for(int i=0;i<n;i++)
#define LOOP(i,x,n) for(int i=x;i<n;i++)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define MP make_pair
#define FIR first
#define SEC second
#define int long long
using namespace std;
const int MOD=1000000007;
const int INF=1000000009;

typedef int Weight;
struct Edge{
  int src;int dst;
  Weight wei;
  Edge(int s=0,int d=0,Weight w=0):
    src(s),dst(d),wei(w){}
};
using Graph = vector<vector<Edge>>;
int prim(const Graph &g,const int r=0){
  struct comp{
    bool operator()(const Edge &e,const Edge &f)const {return e.wei>f.wei;}
  };
  Weight sum=0;
  vector<int> used(g.size());
  priority_queue<Edge,vector<Edge>,comp> q;
  q.emplace(-1,r,0);
  while(q.size()){
    Edge e=q.top();
    q.pop();
    if(used[e.dst])continue;
    used[e.dst]=1;
    sum+=e.wei;
    for(auto &f : g[e.dst]){
      if(!used[f.dst])q.emplace(f);
    }
  }
  return sum;
}

signed main(){
  int n;
  cin>>n;
  Graph g(n);
  REP(i,n)REP(j,n){
    int a;
    cin>>a;
    if(a!=-1){
      g[i].emplace_back(i,j,a);
    }
  }
  cout<<prim(g,0)<<endl;
  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<algorithm>
#include<functional>
#define ll long long
#define inf  999999999
#define pa pair<int,int>

using namespace std;

int n,a[200][200]={0};
void prim(){
	int d[200]={0};
	priority_queue<pair<int,pa> >  PQ; 
	pair<int,pa> q;
	pa r;
	int wei=0;
	int w=6;
	int u=w,z=0;
	d[w]=1;
	while(z!=n-1){
		for(int j=n-1;j>-1;j--){
			if(a[u][j]<=0 && d[j]==0 && u!=j) PQ.push(make_pair(a[u][j],make_pair(u,j)));
		}
	while(1){
		if(PQ.size()==0) {
			cout<<"dv"<<endl;
		break;
		}
		q=PQ.top();
		PQ.pop();
		r=q.second;
	//	cout<<"rsec"<<r.second<<endl;
		if(d[r.second]==0) break;
		
		}
	u=r.second;
//	cout<<"a" <<u<<endl;
	d[u]=1;
	wei=wei+q.first;
	z++;
//	cout<<z<<" "<<-q.first<<" "<<u<<" "<<r.first<<endl;
	
	}
	cout<<-wei<<endl;
}



int main(){
	// your code goes here
	int m;
	cin>>n;
	
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
		cin>>m;
		a[i][j]=-m;
		}
	}
	prim();

	return 0;
}

C++: #include<iostream>
using namespace std;
const int MAX = 100;
const int INF = 20000;
int n, G[MAX][MAX], dis[MAX];
bool book[MAX] = { false };
int main()
{
	cin >> n;
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++)
			cin >> G[i][j];
	for (int i = 0; i < n; i++)
		dis[i] = G[0][i];
	book[0] = true;
	int sum = 0;
	for (int k = 1; k <= n - 1; k++)
	{
		int min = INF;
		int u;
		for (int j = 0; j < n; j++)
			if (!book[j] && dis[j] != -1 && dis[j] < min)
			{
				min = dis[j];
				u = j;
			}
		book[u] = true;
		sum += dis[u];
		for (int v = 0; v < n; v++)
			if (!book[v] && G[u][v] != -1)
				if (dis[v] == -1)
					dis[v] = G[u][v];
				else
					if (dis[v] > G[u][v])
						dis[v] = G[u][v];
	}
	cout << sum << 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;
    // cout<<now<<" "<<q.top().first<<endl;                                                                                                                                                    
    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;

}