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>

using namespace std;

static const int INFTY = 10000000;

int a[124][124] = {{}};
int n;


int prim(){

  int d[124] = {};
  int p[124] = {};
  int flag[124] = {};
  int min = INFTY;
  int u;
  int sum = 0;

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

  d[0] = 0;
  while(1){
    u = -1;
    min = INFTY;
    for(int i = 0;i < n;i++){
      if(flag[i] == 0 && d[i] <= min){
        u = i;
        min = d[i];
      }
    }
    //cout << "u = " << u << endl;
    //cout << "min = " << min << endl;

    if(u == -1) break;
    sum += min;
    flag[u] = 1;

    for(int i = 0;i < n;i++){
      if(flag[i] == 0 && a[u][i] != INFTY){
        if(d[i] > a[u][i]){
          d[i] = a[u][i];
          p[i] = u;
        }
      }
    }
  }
  //for(int i = 0;i < n;i++) if(a[p[i]][i] != INFTY)sum += a[p[i]][i];
  return sum;
}

int main(){

  cin >> n;

  for(int i = 0;i < n;i++){
    for(int j = 0;j < n;j++){
      cin >> a[i][j];
      if(a[i][j] == -1) a[i][j] = INFTY;
    }
  }

  cout << prim() << endl;
}

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++: #include <iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1<<21);
static const int WHITH = 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] = WHITH;
  }

  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>
#include <cstring>
using namespace std;
#define int long long

main(){
  int n;
  cin>>n;
  int a[n][n];
  for(int i=0;i<n;i++)
    for(int j=0;j<n;j++)
      cin>>a[i][j];
  int ans=0;
  bool used[n];
  memset(used,0,sizeof(used));
  used[0]=1;
  int cost[n];
  for(int i=0;i<n;i++) cost[i]=a[0][i];
  while(1){
    int v=-1;
    for(int i=0;i<n;i++){
      if(used[i]||cost[i]<0) continue;
      if(v<0||cost[i]<cost[v]) v=i;
    }
    if(v<0) break;
    used[v]=1;
    ans+=cost[v];
    for(int i=0;i<n;i++){
      if(a[v][i]<0) continue;
      if(cost[i]<0||a[v][i]<cost[i]) cost[i]=a[v][i];
    }
  }
  cout << ans << endl;
}

C++: #include <iostream>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <queue>
#define N 101

using namespace std;

int main () {
  // first 权重，second 顶点 id
  priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > V[N];
  int n, a, T[N], cost = 0, cnt = 0;

  cin >> n;
  
  // 输入为邻接矩阵
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
      cin >> a;

      if (a >= 0) {
        V[i].push(make_pair(a, j));
      }
    }
  }
  
  for (int i = 0; i < N; i++)
    T[i] = 0;

  T[0] = 1;

  while (cnt < n - 1) {
    int minCost = (1 << 21);
    int minI;

    // cout << "cnt = " << cnt << endl;

    for (int i = 0; i < n; i++) {
      if (T[i]) {
        // cout << "i = " << i << endl;
        while (V[i].size() && T[V[i].top().second])
          V[i].pop();

        if (V[i].size() && V[i].top().first < minCost) {
          minCost = V[i].top().first;
          minI = i;
        }
      }
    }

    // cout << minI << " " << V[minI].top().first << " " << V[minI].top().second << endl;

    cost += V[minI].top().first;
    T[V[minI].top().second] = 1;
    V[minI].pop();
    cnt++;
  }

  cout << cost << endl;

  return 0;
}