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>
#include <vector>
#include <utility>
#include <algorithm>
using namespace std;

void init(int n, vector<int>& v){
  v.resize(n);
  for(int i = 0; i < n; i++){
    v[i] = i;
  }
}

int root(int a, vector<int>& v){
  if(v[a] == a) return a;
  return (v[a] = root(v[a], v));
}

bool same(int a, int b, vector<int>& v){
  return root(a,v) == root(b,v);
}

void unite(int a, int b, vector<int>& v){
  v[root(a,v)] = root(b,v);
}


int main(){
  int n;
  cin >> n;
  vector<vector<int> > a(n, vector<int>(n, -1));
  for(int i = 0; i < n; i++)
    for(int j = 0; j < n; j++)
      cin >> a[i][j];

  vector<int> cost, src, dst;
  for(int i = 0; i < n; i++){
    for(int j = i+1; j < n; j++){
      if(a[i][j] > -1){
        cost.push_back(a[i][j]);
        src.push_back(i);
        dst.push_back(j);
      }
    }
  }
  vector<pair<int, int> > edges(cost.size());

  for(int i = 0; i < cost.size(); i++){
    // cout << "cost" << cost[i] << endl;
    // cout << "i" << i << endl;
    edges[i] = make_pair(cost[i], i);
    // cout << edges[i].first << " : " << edges[i].second << endl;
  }

  sort(edges.begin(),edges.end());

  // for(int i = 0; i < cost.size(); i++)
    // cout << edges[i].first << " : " << edges[i].second << endl;

  int sum = 0;
  vector<int> units;
  init(n, units);
  for(int i = 0; i < edges.size(); i++){
    int idx = edges[i].second;
    int s = src[idx], d = dst[idx];
    // cout << s << "," << d << endl;
    if(same(s, d, units))
      continue;
    unite(s, d, units);

    sum += cost[idx];
  }

  cout << sum << endl;
}

C++: #include <iostream>
#include <algorithm>
#include <string>
#include <stack>
#include <cstdlib>
#include <queue>
#include <vector>
#include <set>
#include <stdio.h>
#include <cstdio>
using namespace std;
int p[100001],s[100001],t[10001],cost[10001];
int root(int a) {
	if (p[a] == a) return a;
	return (p[a] = root(p[a]));
}
void unite(int a,int b){
	p[root(a)] = root(b);
}
bool same(int a ,int b){
	if (root(a) == root(b)) return 1;
	else return 0;
}
bool rcheck(int a){
	if (root(a) == a) return 1;
	else return 0;
}
pair <int,int> path[1001];
int main() {
	int n,coun = 0;
	cin >> n;
	for (int i = 0; i < n; i++){
		p[i] = i;
		for (int j = 0;j<n;j++) {
			s[n*i+j] = i; t[n*i+j]=j; 
			cin >> cost[n*i+j];
		}
	}
	for (int i = 0;i < n*n;i++) {
		path[i].first = cost[i];
		path[i].second = i;
	}
	sort(path,path+n*n);
	for (int i = 0; i < n*n;i++) {
		if (path[i].first > 0) {
			if(same(s[path[i].second],t[path[i].second]) == 0) {
				unite(s[path[i].second],t[path[i].second]);
				coun += path[i].first;
			}
		}
	}
	cout << coun << endl;
}

C++: #include <cstdio>
#include <iostream>
#include <vector>
#include <queue>
using namespace std;
int n;
int a[100][100];
int used[100];
int mincost[100];
const int INF=1000000000;
int prim(){
  for(int i=0;i<n;i++){
    used[i]=0;
    mincost[i]=INF;
  }
  mincost[0]=0;
  int res=0;
  while(1){
    int v=-1;
    for(int u=0;u<n;u++){
      if((v==-1 || mincost[v]>mincost[u]) && !used[u])v=u;
    }
    if(v==-1)break;
    used[v]=1;
    res+=mincost[v];
    for(int u=0;u<n;u++){
      mincost[u]=min(mincost[u],a[v][u]);
    }
  }
  return res;
}
int main(){
  scanf("%d",&n);
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      scanf("%d",&a[i][j]);
      if(a[i][j]==-1)a[i][j]=INF;
    }
  }
  printf("%d\n",prim());
  return 0;
}

C++: #include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <queue>
#include <stack>
using namespace std;
const int maxx=110;
const int infinity=(1<<30);

int A[maxx][maxx];
int d[maxx],p[maxx];//d[i]里面存的是V-T中的点，要加入到T中，选取的最小的权值；
					//d[i]=u;表示的是要把V-T中的点i加入到T中所需要的代价是u；
					//p[v]=u;表示的是V-T中的点v，要和T中的点u连接，即u是v的父节点；
bool flag[maxx];	//用flag来标记这个节点是不是在MST中，true是在T里，false是在V-T里；

int main (){
		int n;
		cin>>n;
		for(int i =1;i<=n;i++){
			for(int j=1;j<=n;j++){
				int e;cin>>e;
				A[i][j]=(e==-1)?infinity:e;
			}
		}

		for(int i=0;i<maxx;i++) {
			flag[i]=false;
			d[i]=infinity;
			p[i]=-1;
		}
		int sum=0,minv,minj;
		flag[1]=true;
		while(1){
			minv=infinity;
			minj=-1;
			for(int i=1;i<=n;i++){
				if(flag[i]==true){
					for(int j=1;j<=n;j++){
						if(A[i][j]!=-1 && A[i][j]<minv && flag[j]==false) {
							minv=A[i][j];
							minj=j;
						} 
					}
				}
			}
//			cout<<minv<<endl;
//			cout<<minj<<endl;
			if(minv==infinity || minj==-1) break;
			flag[minj]=true;
			sum+=minv;
		}
		
		cout<<sum<<endl;
		return 0;
		
}

C++: #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 BRACK =2;

int n,A[MAX][MAX];

int prim(){
  int x,minv,d[MAX],p[MAX],c[MAX];

  for(int i=0;i<n;i++){
    d[i]=INF;
    p[i]=-1;
    c[i]=WHITE;
  }

  d[0]=0;
  while(1){
    minv=INF;
    x=-1;
    for(int i=0;i<n;i++){
      if(minv>d[i] && c[i]!=BRACK){
	x=i;
	minv=d[i];
      }
    }
    if(x==-1)break;
    c[x]=BRACK;
    for(int v=0;v<n;v++){
      if(c[v]!=BRACK && A[x][v]!=INF){
	if(d[v]>A[x][v]){
	  d[v]=A[x][v];
	  p[v]=x;
	  c[v]=GRAY;
	}
      }
    }
  }
  int sum=0;
  for(int i=0;i<n;i++){
    if(p[i]!=-1)sum+=A[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;
      A[i][j]=(e==-1)?INF:e;
    }
  }

  cout<<prim()<<endl;
  return 0;
}