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
	for len(edges) > 0 {
		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
	}
	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<vector>
#include<queue>
#include<algorithm>
//#include<operator>

using namespace std;


class UFT{
public:
  int P[10010];//その頂点の親を格納する

  //初めは全ての頂点はバラバラで違うグループに属する
  void init(int N){
    for(int i=0;i<N;i++) P[i]=i;
  }

  int root(int a){
    if(P[a]==a) return a;
    return root(P[a]);
  }

  bool is_same_set(int a,int b){
    return root(a)==root(b);
  }

  void unite(int a,int b){
    //aのルートだったもののルートをbのルートにする
    P[root(a)]=root(b);
  }
};

bool is_same_set_all(UFT a,int n){
  for(int i=0;i<n-1;i++){
    if(!(a.is_same_set(i,i+1))){return false;}
  }
  return true;
}

class edge{
public:
  int from_Node;
  int to_Node;
  int cost;
};

//本来は<さえオーバーロードすれば大丈夫が四つのオペレータをオーバロードしなければならなかった(何故？？)
bool operator< (const edge& e1,const edge& e2){
  return e1.cost < e2.cost;
}


bool operator> (const edge& e1,const edge& e2){
  return e1.cost > e2.cost;
}


bool operator<= (const edge& e1,const edge& e2){
  return e1.cost <= e2.cost;
}

bool operator>= (const edge& e1,const edge& e2){
  return e1.cost >= e2.cost;
}


int main(){
  #if 0
  このようにデバッグができる(比較演算子のオーバーロード)
  edge a={0,1,2},b={1,2,3};
  if(a<b){cout << "a<b" << endl;}
  if(b<a){cout << "b<a" << endl;}
  if(a>b){cout << "a>b" << endl;}
  if(a<=b){cout << "a<=b" << endl;}
  #endif


  int n;cin >> n;
  priority_queue<
  edge,//要素の型
  vector<edge>,//内部コンテナはvectorで(デフォ)
  greater<edge>//昇順
  > ve;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      edge e;int c;
      cin >> c;
      if(c!=-1 and i<j){
        e.from_Node=i;e.to_Node=j;e.cost=c;
        ve.push(e);
      }
    }
  }
  UFT G;G.init(n);
  int co=0;
  while(!(is_same_set_all(G,n))){
    if(!(G.is_same_set(ve.top().from_Node,ve.top().to_Node))){
      G.unite(ve.top().from_Node,ve.top().to_Node);
      co+=ve.top().cost;
      ve.pop();
    }else{
      ve.pop();
    }
  }
  cout << co << endl;

}

C++: #include <bits/stdc++.h>
#define MAX 20000
using namespace std;

int main(void){
  ios::sync_with_stdio(false);
  cin.tie(0);

  int n; cin >> n;
  vector< vector<int> > v(n, vector<int>(n));
  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> v[i][j];
      if(v[i][j] == -1) v[i][j] = MAX;
    }
  }

  vector<int> cost(n, MAX), used(n, false);
  cost[0] = 0;
  int ans = 0;
  int t;

  while(true){
    t = -1;
    for(int i = 0; i < n; i++){
      if(!used[i] && (t == -1 || cost[t] > cost[i])) t = i;
    }
    if(t == -1) break;
    used[t] = true;
    ans += cost[t];

    for(int i = 0; i < n; i++){
      cost[i] = min(cost[i], v[t][i]);
    }
  }

  cout << ans << endl;

  return 0;
}

C++: #pragma region kyomukyomupurin

/**
 *    author  : 𝒌𝒚𝒐𝒎𝒖𝒌𝒚𝒐𝒎𝒖𝒑𝒖𝒓𝒊𝒏
 *    created : 2020-04-24 11:40:03
 **/

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#include <cmath>
#include <complex>
#include <deque>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

using int64 = long long;

template <class T>
using binary_heap = std::priority_queue<T, std::vector<T>, std::greater<T>>;

template <class T, class U>
std::ostream& operator<<(std::ostream& os, const std::pair<T, U>& p) {
  return os << '(' << p.first << ", " << p.second << ')';
}

template <class T>
std::ostream& operator<<(std::ostream& os, const std::vector<T>& vec) {
  int flag = 0;
  for (auto e : vec) os << (flag++ ? ", " : "{") << e;
  return os << '}';
}

template <class T>
std::ostream& operator<<(std::ostream& os, const std::set<T>& st) {
  int flag = 0;
  for (auto e : st) os << (flag++ ? ", " : "{") << e;
  return os << '}';
}

template <class T, class U>
std::ostream& operator<<(std::ostream& os, const std::map<T, U>& mp) {
  int flag = 0;
  for (auto e : mp) os << (flag++ ? ", " : "{") << e;
  return os << '}';
}

template <class T>
std::istream& operator>>(std::istream& is, std::vector<T>& vec) {
  for (T& e : vec) is >> e;
  return is;
}

#define all(_) begin(_), end(_)
#define rall(_) rbegin(_), rend(_)

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]: ", debug_out(__VA_ARGS__)
#else
#define debug(...)
#endif

void debug_out() { std::cerr << '\n'; }

template <class Head, class... Tail>
void debug_out(Head&& head, Tail&&... tail) {
  std::cerr << head;
  if (sizeof...(Tail) != 0) std::cerr << ", ";
  debug_out(std::forward<Tail>(tail)...);
}

#pragma endregion kyomukyomupurin


class UnionFind {
 public:
  UnionFind(int n) : n_(n) { initialize(); }

  int root(int x) {
    assert(0 <= x && x < n_);
    if (parent_[x] == -1)
      return x;
    else
      return parent_[x] = root(parent_[x]);
  }

  bool same(int x, int y) {
    assert(0 <= x && x < n_ && 0 <= y && y < n_);
    return root(x) == root(y);
  }

  void unite(int x, int y) {
    assert(0 <= x && x < n_ && 0 <= y && y < n_);
    x = root(x);
    y = root(y);
    if (x == y) return;
    if (rank_[x] < rank_[y]) std::swap(x, y);
    if (rank_[x] == rank_[y]) ++rank_[x];
    parent_[y] = x;
    return;
  }

 private:
  const int n_;
  std::vector<int> parent_;
  std::vector<int> rank_;

  void initialize() {
    parent_.assign(n_, -1);
    rank_.assign(n_, 0);
  }
};

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  int n; cin >> n;
  vector<vector<int>> a(n, vector<int>(n)); cin >> a;

  vector<pair<int, pair<int, int>>> v;

  for (int i = 0; i < n; ++i) {
    for (int j = i; j < n; ++j) {
      if (a[i][j] == -1) continue;
      v.emplace_back(a[i][j], make_pair(i, j));
    }
  }

  sort(all(v));
  debug(v);

  UnionFind uf(n);

  int ans = 0;

  for (auto e : v) {
    if (uf.same(e.second.first, e.second.second)) continue;
    ans += e.first;
    uf.unite(e.second.first, e.second.second);
  }

  cout << ans << endl;

  return 0;
}