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>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1 << 21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int n, M[MAX][MAX];

int prim() {
	int u, min_value;
	int d[MAX], p[MAX], color[MAX];

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

	d[0] = 0;

	while (true) {
		min_value = INFTY;
		u = -1;
		for (int i = 0; i < n; i++) {
			if (min_value > d[i] && color[i] != BLACK) {
				u = i;
				min_value = d[i];
			}
		}
		if (u == -1) break;
		color[u] = BLACK;
		for (int v = 0; v < n; v++) {
			if (color[v] != BLACK && M[u][v] != INFTY) {
				if (d[v] > M[u][v]) {
					d[v] = M[u][v];
					p[v] = u;
					color[v] = GRAY;
				}
			}
		}
	}
	int sum = 0;
	for (int i = 0; i < n; i++) {
		if (p[i] != -1) sum += M[i][p[i]];
	}

	return sum;
}

int main() {
	cin >> n;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			int e;
			cin >> e;
			M[i][j] = (e == -1) ? INFTY : e;
		}
	}

	cout << prim() << endl;

	return 0;
}

C++: /*
* @Author: Samson
* @Date:   2018-06-12 18:24:44
* @Last Modified by:   Samson
* @Last Modified time: 2018-06-13 11:56:23
*/
//   @URL : http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_12_A
#include<bits/stdc++.h>
#include<algorithm>
#include <cstdlib>
#define white 0
#define gray 1
#define black 2
#define INF 0x3f3f3f3f
using namespace std;
typedef long long LL;
const int MAXN = 1e3+10;

int p[MAXN],color[MAXN],a[MAXN][MAXN],t,n,d[MAXN];

int prim()
{
	int minv,u,v;
	for(int i = 1; i <= n; ++i)
	{
		d[i] = INF;
		p[i] = -1;
		color[i] = white;
	}
	
	d[0] = 0;

	while(1)
	{
		minv = INF;
		u = -1;
		for(int i = 1; i <= n; ++i)
		{
			if(minv > d[i] && color[i] != black)
				minv = d[i],u = i;
		}
		if(u == -1)	break;
		color[u] = black;
		for(int v = 1; v <= n; ++v)
		{
			if(color[v] != black && a[u][v] != INF)
			{
				if(d[v] > a[u][v])
				{
					d[v] = a[u][v];
					p[v] = u;
					color[v] = gray;
				}
			}
		}
	}
	int ans = 0;
	for(int i = 1; i <= n; ++i)
		if(p[i] != -1)
			ans += a[i][p[i]];
	return ans;
}

int main(void)
{
	ios::sync_with_stdio(false); 
	//cin.tie(0);
	cin>>n;
	for(int i = 1; i <= n; ++i)
	{
		for(int j = 1; j <= n; ++j)
		{
			cin>>t;
			a[i][j] = t==-1?INF:t;
		}
	}
	cout<<prim()<<'\n';
	return 0;
}

C++: #include<bits/stdc++.h>
#define ll long long
#define rep(i, n) for(int i=0;i<(n);++i)
#define per(i, n) for(int i=(n)-1;i>=0;--i)
#define repa(i, n) for(int i=1;i<(n);++i)
#define foreach(i, n) for(auto &i:(n))
#define pii pair<int, int>
#define pll pair<long long, long long>
#define all(x) (x).begin(), (x).end()
#define bit(x) (1ll << (x))
const ll MOD = (ll)1e9+7;
const int INF = (ll)1e9+7;
const ll INFLL = (ll)1e18;
using namespace std;
template<class t>
using vvector = vector<vector<t>>;
template<class t>
using vvvector = vector<vector<vector<t>>>;
template<class t>
using priority_queuer = priority_queue<t, vector<t>, greater<t>>;
template<class t, class u> bool chmax(t &a, u b){if(a<b){a=b;return true;}return false;}
template<class t, class u> bool chmin(t &a, u b){if(a>b){a=b;return true;}return false;}

ll modpow(ll x, ll b){
	ll res = 1;
	while(b){
		if(b&1)res = res * x % MOD;
		x = x * x % MOD;
		b>>=1;
	}
	return res;
}

ll modinv(ll x){
	return modpow(x, MOD-2);
}

bool was_output = false;
template<class t>
void output(t a){
	if(was_output)cout << " ";
	cout << a;
	was_output = true;
}
void outendl(){
	was_output = false;
	cout << endl;
}

class minimum_spanning_tree{
public:
	int n;
	vvector<pll> edges;
	minimum_spanning_tree(int N):n(N){
		edges.resize(n);
	}

	void add_edge(int from, int to, ll cost){
		edges[from].emplace_back(to, cost);
	}

	ll solve(){
		ll res = 0;
		priority_queuer<pll> pq;
		pq.emplace(0, 0);
		vector<bool> used(n, false);
		while(pq.size()){
			pll d = pq.top();
			pq.pop();
			if(used[d.second]){
				continue;
			}
			used[d.second] = true;
			res += d.first;
			foreach(i, edges[d.second]){
				if(used[i.first])continue;
				pq.emplace(i.second, i.first);
			}
		}
		return res;
	}
};


int main(){
	int n;
	cin >> n;
	minimum_spanning_tree msp(n);
	rep(i, n){
		rep(j, n){
			int cost;
			cin >> cost;
			if(cost==-1)continue;
			msp.add_edge(i, j, cost);
		}
	}
	cout << msp.solve() << endl;
	return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <vector>

using namespace std;

struct Wside{
	int vertex;
	int weight;
	Wside(int a, int b){
		vertex=a; weight=b;
	}
};

vector<Wside>* info;
vector<int> scanned;
int n;
int minimum;

bool isScanned(int v){
	for(int i=0,sz=scanned.size(); i<sz; ++i){
		if(v==scanned[i]) return 1;
	}
	return 0;
}

int scan(){
	int temp_min=100000;
	int temp_v = 0;
	for(int i=0, sz=scanned.size(); i<sz; ++i){
		int s=scanned[i];
		for(int j=0, sz2=info[s].size(); j<sz2; ++j){
			if(isScanned(info[s][j].vertex)){
				continue;
			}
			temp_min = temp_min<info[s][j].weight? temp_min: info[s][j].weight;
			temp_v = temp_min<info[s][j].weight? temp_v: info[s][j].vertex;
		}
	}

	minimum += temp_min;
	scanned.push_back(temp_v);
	return 0;
}

int main()
{
	scanf("%d",&n);
	info = new vector<Wside> [n];

	int temp;
	for(int i=0; i<n; ++i){
		for(int j=0; j<n; ++j){
			scanf("%d",&temp);
			if(temp!=-1){
				info[i].push_back(Wside(j, temp));
			}
		}
	}

	scanned.push_back(0);
	while(scanned.size()!=n){
		scan();
	}
	cout << minimum << endl;

	delete[] info;

	return 0;
}