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>
#include <cstdio>
#include <string>
#include <list>
#include <stack>
#include <queue>
#include <algorithm>
#include <utility>
#include <vector>
#include <map>

using namespace std;

int main()
{
	int N;
	int maxcost=0;
	vector<pair<int,int> > cost;
	cin>>N;
	vector<int> parent(N,-1);
	pair<int,int> ddata;
	for(int i=0;i<N*N;i++){
		cin>>ddata.first;
		if(ddata.first!=-1){
			ddata.second=i;
			cost.push_back(ddata);
		}
	}
	sort(cost.begin(),cost.end());
	for(int i=0;i<cost.size();i++){
		while(parent[cost[i].second/N]!=-1&&parent[parent[cost[i].second/N]]!=-1){
			parent[cost[i].second/N]=parent[parent[cost[i].second/N]];
		}
		while(parent[cost[i].second%N]!=-1&&parent[parent[cost[i].second%N]]!=-1){
			parent[cost[i].second%N]=parent[parent[cost[i].second%N]];
		}
		if(parent[cost[i].second/N]!=cost[i].second%N&&parent[cost[i].second%N]!=cost[i].second/N&&(parent[cost[i].second%N]!=parent[cost[i].second/N]||parent[cost[i].second/N]==-1||parent[cost[i].second%N]==-1)){
			//cout<<' '<<cost[i].second/N<<' '<<cost[i].second%N<<endl;
			maxcost+=cost[i].first;
			if(parent[cost[i].second/N]==-1){
				if(parent[cost[i].second%N]!=-1){
					parent[parent[cost[i].second%N]]=cost[i].second/N;
				}
				parent[cost[i].second%N]=cost[i].second/N;
			}else if(parent[cost[i].second%N]==-1){
				parent[parent[cost[i].second/N]]=cost[i].second%N;
				parent[cost[i].second/N]=cost[i].second%N;
			}else{
				parent[parent[cost[i].second%N]]=parent[cost[i].second/N];
				parent[cost[i].second%N]=parent[cost[i].second/N];
			}
		}
		int c=0;
		for(int i=0;i<N;i++){
			if(parent[i]==-1){
				c++;
			}
		}
		if(c<2){
			break;
		}
	}
	cout<<maxcost<<endl;
	/*
	for(int i=0;i<N;i++){
		cout<<parent[i]<<endl;
	}//*/
	return 0;
}

C++: #include<iostream>
#include<vector>
using namespace std;
int inf = 10000000;
int n;
int map[101][101];
int dep[101];
int all = 0;
int total = 0;
void solve() {
	vector<int>v;
	v.push_back(0);
	dep[0] = 1;
	total = 1;
	while (total != n)
	{
		int min = inf;
		int k ;
		for (int i = 0; i < v.size(); i++) {
			for (int j = 0; j < n; j++) {
				if (!dep[j] && map[v[i]][j] < min) {
					min = map[v[i]][j];
					k = j;
				}
			}
		}
		v.push_back(k);
		dep[k] = 1;
		all += min;
		total++;
	}
}
int main(void) {
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int k;
			cin >> k;
			map[i][j] = (k == -1) ? inf : k;
		}
	}
	solve();
	cout << all << endl;
}

C++: #include<iostream>
#include<cstdio>
#include<cstdlib>
#include<string.h>
#include<stack>
#include<queue>
#include<vector>
using namespace std;

int n;
int d[10000], m[100][100], p[100];
int c[10000];


void prim(){
  d[0] = 0;
  p[0] = -1;

  while(1){
    int mincost = 10000, u;
    for(int i = 0; i < n; i++){
      if(c[i] != 2 && mincost > d[i]){
        mincost = d[i];
        u = i;
      }
    }

    if(mincost == 10000) break;

    c[u] = 2;

    for(int i = 0; i < n; i++){
      if(c[i] != 2 && m[u][i] >= 0){
        if(m[u][i] < d[i]){
          d[i] = m[u][i];
          p[i] = u;
          c[i] = 1;
        }

      }
    }
  }
}

int main(){

  cin >> n;

  for(int i = 0; i < n; i++){
    c[i] = 0;
    d[i] = 2000;
    for(int j = 0; j < n; j++){
      cin >> m[i][j];
    }
  }

  prim();

  int sum = 0;
  for(int i = 0; i < n; i++) sum += d[i];
  cout << sum << endl;

  return 0;
}