Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

C++: #include<iostream>
#define MAX 100
#define MAXNUM 2001
using namespace std;

int n, M[MAX][MAX];
int u, minv, total = 0;
int w[MAX], p[MAX], color[MAX] = {};

void prim() {
	for (int i = 0; i < n; i++) {
		w[i] = MAXNUM;
		p[i] = -1;
	}
	w[0] = 0;

	while (1) {
		minv = MAXNUM;
		u = -1;
		for (int i = 0; i < n; i++) {
			if (w[i] < minv && color[i] != 2) {
				u = i;
				minv = w[i];
			}
		}
		if (u == -1) break;
		color[u] = 2;
		for (int i = 0; i < n; i++) {
			if (color[i] != 2 && M[u][i] != MAXNUM) {
				if (M[u][i] < w[i]) {
					w[i] = M[u][i];
					p[i] = u;
					color[i] = 1;
				}
			}
		}
	}
}

int main() {
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> M[i][j];
			if (M[i][j] == -1) {
				M[i][j] = MAXNUM;
			}
		}
	}
	prim();
	for (int i = 0; i < n; i++) {
		if (p[i] != -1) total += M[i][p[i]];
	}
	cout << total << endl;
}

C++: #include <iostream>
using namespace std;
#define INF 1000000

int main(){
  long n;
  long G[100][100],d[100];
  long minc,mi,i;
  bool flg[i];
  long sum=0;
  
  cin >> n;
  for (i=0;i<n;i++){
    for (int j=0;j<n;j++){
      cin >> G[i][j];
      if (G[i][j]==-1) G[i][j]=INF;
    }
    d[i]=INF;
    flg[i]=false;
  }

  d[0]=0;
  while (true){
    minc=INF;
    for (i=0;i<n;i++){
      if (!flg[i]&&d[i]<minc){
	minc=d[i];
	mi=i;
      }
    }
    if (minc==INF) break;
    flg[mi]=true;
    for (i=0;i<n;i++){
      if (G[mi][i]==INF)continue;
      if (!flg[i]&&d[i]>G[mi][i]){
	d[i]=G[mi][i];
	//cout << d[i];
      }
    }
  }
  
  for (i=0;i<n;i++){
    sum+=d[i];
  }
  cout << sum<<endl;
  
  return 0;
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;

int x[10000][10000];
int MIN[10000];
int MINX = 0;
int MINZ = 10000000;

int main() {
	memset(MIN, 127, sizeof(MIN));
	int n, a;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> a;
			x[i][j] = a;
		}
	}
	for(int i=0;i<n;i++){
	    for(int j=0;j<n;j++){
	        if(x[i][j]!=-1){
	            MIN[i]=min(x[i][j],MIN[i]);
	        }
	    }
	}
	for(int i=0;i<n;i++){
	    MINX=0;
	    for(int j=0;j<n;j++){
	        MINX += MIN[j];
	    }
	    MINZ=min(MINZ,MINX);
	}
	cout<<MINZ<<endl;
	return 0;
}

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

// 総数を1000000007で割った余り
const long long mod = 1e9 + 7;

using ll  = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
#define ull unsigned long long
#define ld long double
#define vi vector<int>
#define vll vector<ll>
#define vc vector<char>
#define vs vector<string>
#define vpii vector<pii>
#define vpll vector<pll>

#define rep(i, n) for (int i = 0, i##_len = (n); i < i##_len; i++)
#define rep1(i, n) for (int i = 1, i##_len = (n); i <= i##_len; i++)
#define repr(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define rep1r(i, n) for (int i = ((int)(n)); i >= 1; i--)

#define sz(x) ((int)(x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()

#define SORT(v, n) sort(v, v + n);
// #define SORT(v, n) stable_sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define RSORT(x) sort(rall(x));
#define pb push_back
#define mp make_pair

#define PI (acos(-1))
#define EPS (1e-7)

ull gcd(ull a, ull b) { return b ? gcd(b, a % b) : a; }
ull lcm(ull a, ull b) { return a / gcd(a, b) * b; }

const int MAX   = 100;
const int INF   = (1 << 21);
const int white = 0;
const int gray  = 1;
const int black = 2;

int n, m[MAX][MAX];

int prim() {
    int u, minV;
    int d[MAX], p[MAX], color[MAX];
    rep(i, n) {
        d[i]     = INF;
        p[i]     = -1;
        color[i] = white;
    }

    d[0] = 0;
    while (1) {
        minV = INF;
        u    = -1;
        rep(i, n) {
            if (minV > d[i] && color[i] != black) {
                u    = i;
                minV = d[i];
            }
        }
        if (u == -1) break;
        color[u] = black;
        rep(v, n) {
            if (color[v] != black && m[u][v] != INF) {
                if (d[v] > m[u][v]) {
                    d[v]     = m[u][v];
                    p[v]     = u;
                    color[v] = gray;
                }
            }
        }
    }
    int sum = 0;
    rep(i, n) {
        if (p[i] != -1) sum += m[i][p[i]];
    }
    return sum;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    // cout << fixed << setprecision(5);

    cin >> n;
    rep(i, n) {
        rep(j, n) {
            int e;
            cin >> e;
            m[i][j] = (e == -1) ? INF : e;
        }
    }
    cout << prim() << endl;

    return 0;
}

C++: // Graph II - Minimum Spanning Tree
// 問題URL: http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=ALDS1_12_A&lang=jp
//
// 使うライブラリも多く、難しく感じた...
#include <iostream>
#include <algorithm>

using namespace std;

int n, buff, cost[101][101]={}, P[101], M = 0, ans = 0;
pair<int, int> edges[10010], vertices[10010];

void init(int n){
  for(int i = 0; i < n; ++i){
    P[i] = i;
  }
}

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

bool is_same_set(int x, int y){
  return root(x) == root(y);
}

void unite(int x, int y){
  P[root(x)] = root(y);
}

int main(){
  cin >> n;

  for(int row = 0; row < n; ++row){
    for(int col = 0; col < n; ++col){
      cin >> buff;
      cost[row][col] = buff; //隣接行列の読込
    }
  }

  for(int row = 0; row < n; ++row){
    for(int col = 0; col < row; ++col){
      if(cost[row][col]>0){
        edges[M].first = cost[row][col];
        edges[M].second = M;
        // cout << M << ": (" << row << ", " << col << ") = " << edges[M].first << endl;
        vertices[M].first = row, vertices[M].second = col;
        M++; //辺の数を管理、idとして利用
      }
    }
  }

  init(n);

  sort(edges, edges+M); //重みの小さい順に整列

  for(int i = 0; i <= M; ++i){
    int index = edges[i].second; //辺のidを取り出す
    if(!is_same_set(vertices[index].first, vertices[index].second)){ //辺の両端が繋がっていなければ
      unite(vertices[index].first, vertices[index].second); //両端を繋げる
      // cout << "unite " << vertices[index].first << " and " << vertices[index].second << endl;
      ans += edges[i].first; //コストを加える
    }
  }
  cout << ans << endl;
}