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 <stdio.h>
#include <stdint.h>
#include <iostream>
#include <fstream>
#include <cassert>
#include <climits>

#include <vector>
#include <string>
using namespace std;

#define DEBUG (0)

#if DEBUG
#define DPRINTF(...) do { \
    printf("D(L%d) %s: ", __LINE__, __func__); \
    printf(__VA_ARGS__); \
  } while (false)
#else
#define DPRINTF(...)
#endif // DEBUG

/*
   recursive + dfs
*/

const uint8_t kMaxN = 100;
int16_t gWeightOfVij[kMaxN][kMaxN];
int gNumOfVertices;


void printAllWeights()
{
  DPRINTF("Number of vertices %d\n", gNumOfVertices);

  for (int i = 0; i < gNumOfVertices; i++)
  {
    for (int j = 0; j < gNumOfVertices; j++)
    {
      if (j == 0)  DPRINTF("");
      printf(" %d", gWeightOfVij[i][j]);
    }
    cout << endl;
  }
}


void printAllPath()
{
  DPRINTF("Number of vertices %d\n", gNumOfVertices);

  for (int i = 0; i < gNumOfVertices; i++)
  {
    for (int j = 0; j < gNumOfVertices; j++)
    {
      if (gWeightOfVij[i][j] > 0)
        printf("%d -> %d (%d)\n", i, j, gWeightOfVij[i][j]);
    }
  }
}


vector<int16_t> getConnectedVs(int16_t v, const bool visited[])
{
  vector<int16_t> vertices;

  for (int i = 0; i < gNumOfVertices; i++)
  {
    if (gWeightOfVij[v][i] > 0 && !visited[i])
      vertices.push_back(i);
  }

#if 0
  if (vertices.size() > 0)
  {
    for (int i = 0; i < vertices.size(); i++)
    {
      if (i == 0)
        DPRINTF("v from %d to :", v);

      printf(" %d", vertices[i]);
    }

    cout << endl;
  }
#endif

  return vertices;
}


int minSpanningTreeRecursive(int16_t currentV, const bool visited[], string inpPath, string &minPath)
{
  assert(0 <= currentV && currentV < gNumOfVertices);

  bool updatedVisited[gNumOfVertices];

  for (int i = 0; i < gNumOfVertices; i++)
    updatedVisited[i] = visited[i];

  updatedVisited[currentV] = true;

  // This function ensures all of elements are unvisited
  vector<int16_t> nextVs = getConnectedVs(currentV, updatedVisited);

  if (nextVs.size() == 0)
  {
    minPath = to_string(currentV);
    return 0;
  }

  int minV = -1;
  int minScore = INT_MAX;
  string currentPath = to_string(currentV);


  if (inpPath.size())
    currentPath = inpPath + " > " + currentPath;

  for (int i = 0; i < nextVs.size(); i++)
  {
    string searchedPath = "";
    const int16_t nextV = nextVs[i];
    const int score = gWeightOfVij[currentV][nextV] + minSpanningTreeRecursive(nextV, updatedVisited, currentPath, searchedPath);

    if (minScore > score)
    {
      minV = nextV;
      minScore = score;
      minPath = searchedPath;
    }

  }

  {
    if (minPath.size())
      minPath = " > " + minPath;

    minPath = to_string(currentV) + minPath;

    DPRINTF("score %d\n", minScore);
    DPRINTF("  %s | %s\n", currentPath.c_str(), minPath.c_str());
  }

  return minScore;
}


int minSpanningTree()
{
  int16_t startV = 0;
  bool visited[gNumOfVertices];

  for (int i = 0; i < gNumOfVertices; i++)
    visited[i] = false;

  string inpPath = "", minPath;

  return minSpanningTreeRecursive(startV, visited, inpPath, minPath);
}


int main()
{
  cin >> gNumOfVertices; cin.ignore();

  DPRINTF("Number of vertices %d\n", gNumOfVertices);

  for (int i = 0; i < gNumOfVertices; i++)
  {
    for (int j = 0; j < gNumOfVertices; j++)
      cin >> gWeightOfVij[i][j];

    cin.ignore();
  }

#if DEBUG
  DPRINTF("Number of vertices %d\n", gNumOfVertices);
  //printAllWeights();
  printAllPath();
#endif // DEBUG

  cout << minSpanningTree() << endl;

  return 0;
}