Go: package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

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

using namespace std;




struct link { //link connecting x and y vertices
  int x;
  int y;
  int weight;
  bool operator<(const link& other) const
  {
    return weight > other.weight; // for min priority queue, trick the operator
  }
};

priority_queue<link> links;
int roots[100];

int root(int x) {
  if (x == roots[x]) {
    return x;
  } else {
    roots[x] = root(roots[x]); //attach all to root
    return root(roots[x]);
  }
}

bool same(int x, int y) {
  return (root(x) == root(y));
}

void unite(int x, int y) {
  roots[root(x)] = root(y);
}


  
int main() {
  int min_cost = 0;
  int n;
  cin >> n;


  for (int i = 0; i < n; i++) {
    roots[i] = i; // initialize roots
    for (int j = 0; j < n; j++) {
      
      int weight;
      cin >> weight;
      if (j <= i ) continue;
      if (weight != -1) {
	link new_link = {i, j, weight};
	links.push(new_link);
	//cout << "link added has i j weight: " << i << " " << j << " " << weight << endl;
      }
    }
  }

  while (!links.empty()) {
    link cur_link = links.top();
    //cout << "cur link weight: " << cur_link.weight << " x: " << cur_link.x << " y: " << cur_link.y << endl;
    if (!same(cur_link.x, cur_link.y)) {
      min_cost += cur_link.weight;
      unite(cur_link.x, cur_link.y);
    }
    links.pop();
  }

  cout << min_cost << endl;
      
    
}

C++: #include <iostream>
#include <limits>
using namespace std;
#define MAX 100
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;

int n,d[MAX+10],p[MAX+10],color[MAX+10];
int W[MAX+10][MAX+10];

int prim()
{
  int v,k,mini,flag,u=0;
  for(int i=0;i<n;i++)
  {
      d[i]=INT_MAX;
      p[i]=-1;
  }
  d[0]=0;
  while(1)
  {
      mini=INT_MAX;
      flag=1;
      for(int i=0;i<n;i++)
      {
          if(d[i]<mini&&color[i]!=BLACK)
          {
              u=i;
              mini=d[i];
              flag=0;
          }
      }
      if(flag) break;
      color[u]=BLACK;
      for(v=0;v<n;v++)
      {
          if(W[u][v]!=INT_MAX&&color[v]!=BLACK)
          {
            if(d[v]>W[u][v])
            {
              d[v]=W[u][v];//更新当前点到最小生成树的距离
              p[v]=u;//每一轮都需要跑更新前驱结点
            }
          }
      }
  }
  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++)
    {
        for(int j=0;j<n;j++)
        {
         int e;
         cin>>e;
         W[i][j]=(e==-1)?INT_MAX:e;
        }
        color[i]=WHITE;
    }
    cout<<prim()<<endl;
}

C++: #include<stdio.h>

#define INFTY 10000
#define black 2
#define gray 1
#define white 0
#define MAX 100

int n,A[MAX][MAX];

int prim()
{
  int i,v,u,min_v;
  int a[MAX],b[MAX],IRO[MAX];

  for(i=0;i<n;i++)
    {
      a[i] = INFTY;
      b[i] = -1;
      IRO[i] = white;
    }

  a[0] = 0;

  while(1)
    {
      min_v = INFTY;
      u = -1;
      for(i=0;i<n;i++)
	{
	  if(min_v > a[i] && IRO[i] != black)
	    {
	      u = i;
	      min_v = a[i];
	    }
	}
      if(u==-1) break;
      IRO[u] = black;
      for(v=0;v<n;v++)
	{
	  if(IRO[v] != black && A[u][v] != INFTY)
	    {
	      if(a[v]>A[u][v])
		{
		  a[v]=A[u][v];
		  b[v] = u;
		  IRO[v] = gray;
		}
	    }
	}
    }
  int sum =0;

  for(i=0;i<n;i++)
    {
      if(b[i] != -1) sum += A[i][b[i]];
    }

  return sum;
}

int main()
{
  int e,i,j;
  scanf("%d",&n);

  for(i=0;i<n;i++)
    {
      for(j=0;j<n;j++)
	{
	  scanf("%d",&e);
	  A[i][j] = (e==-1) ? INFTY : e;
	}
    }
  printf("%d\n",prim());


  return 0;
}

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

const int MAX = 100;
const int INFINITY = 2 << 21;
int n;
int G[MAX][MAX];
int distances[MAX];
int parents[MAX];
int states[MAX];

int prim() {
  int id = 0;
  distances[id] = 0;

  while (1) {
    int min = INFINITY;

    for (int i = 0; i < n; i++) {
      if (states[i] == 0 && distances[i] < min) {
        min = distances[i];
        id = i;
      }
    }

    if (min == INFINITY) break;

    for (int i = 0; i < n; i++) {
      if (G[id][i] == -1) continue;
      if (G[id][i] < distances[i]) {
        distances[i] = G[id][i];
        parents[i] = id;
      }
    }

    states[id] = 1;
  }

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

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  cin >> n;

  for (int i = 0; i < n; i++) {
    distances[i] = INFINITY;
    parents[i] = -1;
    states[i] = 0;
    for (int j = 0; j < n; j++) {
      cin >> G[i][j];
    }
  }

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

C++: #include <iostream>
#include <queue>
#include <climits>
using namespace std;

const int N = 100;
int n;
int A[N][N];
priority_queue< pair<int, int> > Q;

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

	int mcost = -INT_MAX;

	for (int i=0; i<n; i++)
	{
		bool visit[N] = {0};

		Q.push(pair<int, int>(0,i));

		int cost = 0;

		while (Q.size())
		{
			pair<int, int> q = Q.top();
			Q.pop();
			int k = q.second;
			if (visit[k]) continue;
			cost += q.first;
			visit[k]=true;
			for(int j=0;j<n;j++)
			{
				int c = A[k][j];
				if (c <= 0) continue;
				if (visit[j]) continue;
				Q.push(pair<int, int>(-c,j));
			}
		}

		cout << i << ' ' << -cost << endl;

		if (mcost < cost) mcost = cost;
	}

	cout << -mcost << endl;
		
	return 0;
}