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>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define repr(i, n) for (int i = (n); i >= 0; --i)
#define FOR(i, m, n) for (int i = (m); i < (n); ++i)
#define FORR(i, m, n) for (int i = (m); i >= (n); --i)
using namespace std;
typedef long long ll;
const ll mod = 1000000007;
const ll mod2 = 998244353;

const int MAX = 105;
const int INF = 1000000007;
const int white = 0;
const int gray = 1;
const int black = 2;

int n, M[MAX][MAX];

int prim() {
  int u, minv;
  int d[MAX], p[MAX], color[MAX];
  rep(i, n) {
    d[i] = INF;
    p[i] = -1;
    color[i] = white;
  }
  d[0] = 0;
  while (1) {
    minv = INF;
    u = -1;
    rep(i, n) {
      if (minv > d[i] && color[i] != black) {
        u = i;
        minv = d[i];
      }
    }
    if (u == -1) break;
    color[u] = black;
    rep(v, n) {
      if (color[v] != black && M[u][v] != INF) {
        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) ? INF : e;
    }
  }
  cout << prim() << endl;

  
  return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
constexpr int INF = (1 << 30) - 1;

int n;
int dist[105][105];

int prim()
{
    int d[105];
    bool flag[105] = {};
    int cnt = 0, sum = 0;
    fill_n(d, 105, INF);
    d[0] = 0;
    
    while ( true ) {
        int u = -1;
        for ( int i = 0; i < n; i++ ) {
            if ( !flag[i] && (u == -1 || d[u] > d[i] ) ) u = i;
        }
        
        flag[u] = true;
        sum += d[u];
        cnt++;
        if ( cnt == n ) break;

        for ( int i = 0; i < n; i++ ) {
            if ( !flag[i] && dist[u][i] != -1 && d[i] > dist[u][i] ) {
                d[i] = dist[u][i];
            }
        }
    }

    return ( sum );
}

int main()
{
    cin >> n;
    for ( int i = 0; i < n; i++ ) {
        for ( int j = 0; j < n; j++ ) {
            cin >> dist[i][j];
        }
    }
    cout << prim() << endl;
    return ( 0 );
}

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

#define WHITE 1
#define BLACK 2
#define GRAY 3
#define M 100
#define INFTY (1<<21)

int n,color[M],A[M][M];

int prim(){
  int d[M],p[M],u = -1,min;

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

  while(1){
    min = INFTY;
    u = -1;
    for(int i = 0;i < n;i++){
      if(color[i] != BLACK && d[i] < min){
        min = d[i];
        u = i;
      }
    }
    if(u == -1) break;

    color[u] = BLACK;

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

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

  return re;
}

int main(){

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

  cout << prim() << endl;

  return 0;
}

C++: #include <algorithm>
#include <cstdint>

using namespace std;

enum status_t {
  WHITE,
  GRAY,
  BLACK,
};

#define GRAPH_SIZE 101

static uint32_t graph[GRAPH_SIZE][GRAPH_SIZE];
static status_t state[GRAPH_SIZE];
static uint32_t shortest_path[GRAPH_SIZE];

size_t minimum_spanning_tree(size_t num)
{
  size_t minimum_cost = 0;

  for (uint32_t i = 0; i < num; i++) {
    shortest_path[i] = UINT32_MAX;
    state[i] = WHITE;
  }

  shortest_path[0] = 0;
  state[0] = GRAY;

  while (true) {
    uint32_t minimum = UINT32_MAX;
    uint32_t to = 0;
    for (uint32_t j = 0; j < num; j++) {
      if ((shortest_path[j] < minimum) && state[j] != BLACK) {
        minimum = shortest_path[j];
        to = j;
      }
    }

    if (minimum == UINT32_MAX) break;

    state[to] = BLACK;
    minimum_cost += minimum;

    for (uint32_t j = 0; j < num; j++) {
      if ((graph[to][j] != UINT32_MAX) && (state[j] != BLACK)) {
        state[j] = GRAY;
        shortest_path[j] = min(shortest_path[j], graph[to][j]);
      }
    }
  }

  return minimum_cost;
}

#include <iostream>

int32_t main()
{
  uint32_t num;
  cin >> num;

  for (uint32_t i = 0; i < num; i++) {
    for (uint32_t j = 0; j < num; j++) {
      int32_t val;
      cin >> val;
      if (val == -1) {
        graph[i][j] = UINT32_MAX;
      } else {
        graph[i][j] = val;
      }
    }
  }

  cout << minimum_spanning_tree(num) << endl;

  return 0;
}