Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] >= 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A >= edges[j].A })

	sum := 0
	num := 0
	for len(edges) > 0 && num < n-1 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
		num += 1
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

C++: #include <iostream>
#include <utility>
#include <string>
#include <algorithm>
#include <set>
#include <deque>
#include <vector>
#define MAX 150
#define rep(i,p) for(int i=0;i<p;i++)
#define rep1(i,p) for(int i=1;i<=p;i++)
#define pb push_back
using namespace std;
int n,temp,a,b,size;
int A[MAX];
int B[MAX];
int W[MAX];
int V[MAX];
pair<int,int> edge[MAX];

int root (int child) {
  int a = child;
  while (V[a] != a) {
    a = V[a];
  }
  return a;
}

int main(){
  size = 0;
  cin >> n;
  rep(i,n) 
    rep(j,n) {
      cin >> W[size];
      if (i <= j) {        
        A[size] = i;
        B[size] = j;
        edge[size].first = W[size];
        edge[size].second = size;
        size++;
      }
    }

  // sort by lenght of edge
  sort(edge, edge+size+1);
  // printing
  // rep(i,size+1) {
  //   cout << A[edge[i].second] << " " << B[edge[i].second]
  //        << " " << edge[i].first << endl;;
  // }
  int sum = 0;
  rep(i,n) V[i] = i;
  rep(i,size) {
    if (edge[i].first == -1) continue;
    temp = edge[i].second;
    // a , b : vertex
    a = A[temp]; 
    b = B[temp];
    if (root(a) != root(b)) {
      // ?????????????????????
      sum += edge[i].first;
      if (root(a) != a && root(b) == b){        
        V[b] = a;
      } else if (root(a) == a && root(b) != b) {
        V[a] = b;
      } else if (root(a) == a && root(b) == b) {        
        V[a] = b;
      }
    } else {
    }
  }
  cout << sum << endl;
  return 0;
}

C++: //Minimum Spannig Tree
#include <iostream>
#include <vector>
#include <climits>

using namespace std;

static const int N = 100;
static const int WHITE = 0;
static const int BLACK = 1;

int prim(vector<vector<int>> &G, int n) {
    int colors[n], d[n];
    for(int i = 0; i < n; i++) {
        colors[i] = WHITE;
        d[i] = INT_MAX;
    }

    d[0] = 0;
    int l = 0;
    while(1) {
        int u = -1;
        int mincost = INT_MAX;
        for(int i = 0; i < n; i++) {
            if(colors[i] == WHITE && d[i] < mincost) {
                mincost = d[i];
                u = i;
            }
        }
        if(u == -1) break;
        colors[u] = BLACK;
        l += mincost;
        for(int v = 0; v < n; v++)
            if(colors[v] == WHITE && G[u][v] != -1)
                if(G[u][v] < d[v])
                    d[v] = G[u][v];
    }
    return l;
}

int main() {
    int n;
    cin >> n;
    vector<vector<int>> G(n, vector<int>(n));
    for(int i = 0; i < n; i++)
        for(int j = 0; j < n; j++)
            cin >> G[i][j];

    cout << prim(G, n) << endl;
}