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<stdio.h>
#include<limits.h>
#define NIL -1
static const int MAX = 500;
static const int INFTY = (1<<21);
int n, i, j, e, v, sum, u , minV;
main(){
 
  int M[MAX][MAX], key[MAX], L[MAX],A[MAX];
  
  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;
    }
  }

  for(i = 0; i < n; i++){
    key[i] = INT_MAX;
    L[i] = NIL;
    A[i] = NIL;
  }
  
  key[0]=0;
  
  for(;;){
    
    u = NIL;
    
    minV = INT_MAX;
    
    for(i = 0;  i < n; i++){
      
      if(key[i] < minV && A[i] == NIL){
        
        u = i;
        
        minV = key[i];
        
      }
      
    }  
    if(u == NIL)break;
    
    A[u] = u; 
    
    for(v = 0; v < n; v++){
      if(M[u][v] < key[v] && A[v] == NIL){
        key[v] = M[u][v];
        L[v] = u;
      }
    }
  }
  
  sum = 0;
  
  for ( i = 0; i < n; i++ ){
    if ( L[i] != -1 ) sum +=M[L[i]][i];
  }
  
  printf("%d\n", sum);
  
  
  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;
}

C++: //
// Created by 李青坪 on 2018/11/6.
//

#include <cstdio>
#include <algorithm>
#include <set>
#define MAXN 100
#define INFINITY 1<<20
#define NIL -1
using namespace std;

int n;
int sum;
int graph[MAXN][MAXN];
int d[MAXN];
int parent[MAXN];
set<int> T;
set<int> V_T;

void init(){
    fill(d, d+n, INFINITY);
    fill(parent, parent+n, NIL);
    T.insert(0);
    for (int i = 1; i < n; ++i) {
        V_T.insert(i);
    }
    for (int j = 0; j < n; ++j) {
        d[j] = graph[0][j];
    }
}

void updateMinWeight(){

}

pair<int, pair<int, int> > findMinEdge(){
    int min = INFINITY;
    pair<int, int> r;
    set<int >::iterator itr;
    for (itr = T.begin(); itr != T.end(); itr++){
        for (set<int>::iterator itr1 = V_T.begin(); itr1 != V_T.end(); itr1++){
            if (graph[*itr][*itr1] < min){
                min = graph[*itr][*itr1];
                r = make_pair(*itr, *itr1);
            }
        }
    }
    return make_pair(min, r);
}

void findMinSpanTree(){
    while (!V_T.empty()){
        pair<int, pair<int, int> > v = findMinEdge();
        sum += v.first;
        parent[v.second.second] = v.second.first;
        T.insert(v.second.second);
        V_T.erase(V_T.find(v.second.second));
    }
}

int main(){
    scanf("%d", &n);
    for (int i = 0; i < n; ++i) {
        int w;
        for (int j = 0; j < n; ++j) {
            scanf("%d", &w);
            if (w == -1) graph[i][j] = INFINITY;
            else graph[i][j] = w;
        }
    }
    init();
    findMinSpanTree();
    printf("%d\n", sum);
}
/*
5
 -1 2 3 1 -1
 2 -1 -1 4 -1
 3 -1 -1 1 1
 1 4 1 -1 3
 -1 -1 1 3 -1
 */

C++: #include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007
#define INF (1<<21)
#define white 0
#define gray 1
#define black 2

int n;
int W[100][100];
int color[100],d[100],p[100];

int prim() {

  d[0] = 0;

  while(true) {
    int mini = INF,u;
    for(int i = 0;i < n;i++) {
      if(d[i] < mini && color[i] != black) {
        mini = d[i];
        u = i;
      }
    }

    

    if(mini == INF) break;
    color[u] = black;

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

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

}


int main() {

  cin >> n;

  for(int i = 0;i < n;i++) {
    color[i] = white;
    d[i] = INF;
    p[i] = -1;
    for(int j = 0;j < n;j++) {
      int a;
      cin >> a;
      W[i][j] = a;
    }
  }

 
    cout << prim() << endl;

}