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;
  static const int MAX=100;
  static const int INF=(1<<21);
  static const int WHI=0;
  static const int GRA=1;
  static const int BLA=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]=INF;
      p[i]=-1;
      color[i]=WHI;
    }
    
    d[0]=0;
    while(1){
      minv=INF;
      u=-1;
      for(int i=0;i<n;i++){
	if(minv>d[i]&&color[i]!=BLA){
	  u=i;
	}
      }

      if(u==-1){
	break;
      }
      color[u]=BLA;

      for(int v=0;v<n;v++){
	if(color[v]!=BLA&&M[u][v]!=INF){
	  if(M[u][v]<d[v]){
	    d[v]=M[u][v];
	    p[v]=u;
	    color[v]=GRA;
	  }

	}
      }
    }

    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;
	if(e==-1){
	  M[i][j]=INF;
	}else{
	  M[i][j]=e;
	}
      }
    }
    
    cout<<prim()<<endl;
    return 0;
  }

C++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

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];

   // 初期化
   rep(i, n) {
      d[i] = INFTY;
      p[i] = -1;
      color[i] = WHITE;
   }

   d[0] = 0;

   while(1) {
      minv = INFTY;
      u = -1;

      rep(i, n){
         if (minv > d[i] && color[i] != BLACK) {
            u = i;
            minv = d[i];
         }
      }
      if(u == -1) break;
      // uの決定
      color[u] = BLACK;

      rep(v, n) {
         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;
   rep(i, n) {
      if(p[i] != -1) sum += M[i][p[i]];
   }
   return sum;
}

int main(){
   cin >> n;
   rep(i, n) {
      rep(j, n) {
         int e; cin >> e;
         M[i][j] = (e == -1) ? INFTY : e;
      }
   }

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

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
#include <iostream>
#include <list>
#include <cstdio>
#include <cmath>
#include <cstring>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <iomanip>
#define INF 2147483647
 
using namespace std;

#define MAX_V 101

int G[MAX_V][MAX_V];  // cost[u][v]は辺e=(u,v)のコスト(存在しない場合はINF)
int mincost[MAX_V];      // 集合Xからの辺の最小コスト
bool used[MAX_V];        // 頂点iがXに含まれているか
int V;                   // 頂点数

int prim(int n)
{
	
	V = n;

	for (int i = 0; i < V; i++) {
		mincost[i] = INF;
		used[i] = false;
	}

	int res = 0;
	mincost[0] = 0;

	while (true) {
		int v = -1;
		for (int u = 0; u < V; u++) {
			if (!used[u] && (v == -1 || mincost[u] < mincost[v])) v = u;
		}
		if (v == -1) break;
		used[v] = true;     // 頂点vをXに追加
		res += mincost[v];  // 辺のコストを加える
		for (int u = 0; u < V; u++) {
			mincost[u] = min(mincost[u], G[v][u]);
		}
	}

	return (res);
}


int main(void)
{
	int n;

	cin >> 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] = INF; 
		}
	}

	cout << prim(n) << endl;


	return (0);
}

C++: #include <iostream>
#include <climits>
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;
}