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 <bits/stdc++.h>
using namespace std;

const int MAX=105;
int state[MAX],N,S[MAX][MAX];
priority_queue<pair<int,int>> Q;

int prim(){
    int sum=0,cnt=1;
    for(int i=0;i<N;i++){
        state[i]=0;
    }
    state[0]=1;
    for(int i=0;i<N;i++){
        if(S[0][i]!=10000) Q.push(make_pair(-S[0][i],i));
    }
    while(1){
        int a=Q.top().second;
        if(state[a]==0){
        sum+=(-Q.top().first);
        Q.pop();
        state[a]=1;
        cnt++;
        for(int i=0;i<N;i++){
            if(S[a][i]!=10000000&&state[i]==0) Q.push(make_pair(-S[a][i],i));
        }
        }
        else Q.pop();
        if(cnt==N) break;
    }
    return sum;
}


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) S[i][j]=10000000;
            else S[i][j]=a;
        }
    }
    cout<<prim()<<endl;
}

C++: #include<iostream>
#include<vector>
#include<queue>
using namespace std;
enum COLOR{WHITE, BLACK};

struct Edge{
    int w;
    int i;
    int j;
    Edge(int w_, int i_, int j_) : w(w_), i(i_), j(j_) {}
    bool operator< (const Edge& right) const{
        return w > right.w;
    }
};

int main(){
    int n;
    cin >> n;
    vector<vector<int> > G(n, vector<int>(n));
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> G[i][j];
            if (G[i][j] == -1) G[i][j] = 1e8;
        }
    }
    vector<COLOR> state(n, WHITE);
    priority_queue<Edge> prim;
    state[0] = BLACK;
    int sum = 0;
    int idx_new_gray = 0;
    for (int i = 1; i < n; i++) {
        for (int j = 0; j < n; j++) {
            if (state[j] != WHITE) continue;
            prim.push(Edge(G[idx_new_gray][j], idx_new_gray, j));
        }
        while (state[prim.top().j] == BLACK) prim.pop();
        sum += G[prim.top().i][prim.top().j];
        state[prim.top().j] = BLACK;
        idx_new_gray = prim.top().j;
        prim.pop();
    }
    cout << sum << 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,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++: //
//  ALDS_12_A.cpp
//  
//
//  Created by 杵鞭俊 on 2018/07/24.
//

#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 <iostream>
using namespace std;

static const int MAX = 100;
static const int UNVISITED = 0;
static const int VISITING = 1;
static const int VISITED = 2;

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


int n, M[MAX][MAX];

int prim()
{
	int d[MAX], p[MAX];
    
	for(int i = 0;i < n;i++)
	{
	  d[i]=INFTY; 
	  p[i]=0;
	}
	
	d[0]=-1;//加入第一个点，-1表示该点在集合U中，否则在集合V中
	int num = 0,ans = 0, e = 0;//e为最新加入集合的点
    while(num < n-1)//加入m-1条边
   {
	int micost=INFTY,miedge=-1;
	for(int i=0;i<n;i++)
		if(d[i]!=-1)
		{
			int temp=M[e][i];
			if(temp<d[i])
			{
				d[i]=temp;
				p[i]=e;
			}
			if(d[i]<micost)
				micost=d[miedge=i];
		}

	ans+=micost;
	d[e=miedge]=-1;
	num++;
	}
	return ans;
}

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;
}