Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

const BIG_COST = 3000

const (
	ST_NOT_YET = iota
	ST_JOINED
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	costs := make([][]int, nNodes)

	for r := 0; r < nNodes; r++ {
		costs[r] = make([]int, nNodes)
		for c := 0; c < nNodes; c++ {
			costs[r][c] = scanInt(sc)
		}
	}

	states := make([]int, nNodes)
	minCosts := make([]int, nNodes)

	for i := 1; i < nNodes; i++ {
		minCosts[i] = BIG_COST
	}

	for {
		var u int
		minCost := BIG_COST

		for i := 0; i < nNodes; i++ {
			if states[i] != ST_JOINED && minCosts[i] < minCost {
				minCost = minCosts[i]
				u = i
			}
		}

		// 全てのノードが MST に JOIN できたので終了。
		if minCost == BIG_COST {
			break
		}

		states[u] = ST_JOINED

		for v := 0; v < nNodes; v++ {
			cost := costs[u][v]

			// MST内の u と MST外の v との辺の重みをそれぞれ minCosts[v] として
			// 保存しておく。このうち辺の重みが最小となる v が次のループで MST に JOIN する。
			if states[v] != ST_JOINED && cost != -1 && cost < minCosts[v] {
				minCosts[v] = cost
			}
		}
	}

	sum := 0
	for _, cost := range minCosts {
		sum += cost
	}
	fmt.Println(sum)
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

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;
}

C++: #include<bits/stdc++.h>

using namespace std;

int mat[110][110];

typedef pair<int,int> P;

P edge[10010];

bool cmp(P a,P b)
{
    return mat[a.first][a.second]>mat[b.first][b.second];
}

int p[110];

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

int fnd(int x)
{
    if(p[x]!=x)
    {
        p[x]=fnd(p[x]);
    }
    return p[x];
}

bool unit(int a,int b)
{
    int fa=fnd(a),fb=fnd(b);

    if(fa!=fb)
    {
        p[fa]=fb;
    }
}

bool same(int a,int b)
{
    return fnd(a)==fnd(b);
}

int main()
{

    int n;
    cin>>n;

    int cnt=0;

    init(n);
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cin>>mat[i][j];

            if(mat[i][j]!=-1)
            {
                edge[cnt++]=make_pair(i,j);
            }
        }
    }

    sort(edge,edge+cnt,cmp);

    int ans=0;
    while(cnt--)
    {
        P tmp=edge[cnt];

        if(!same(tmp.first,tmp.second))
        {
            ans+=mat[tmp.first][tmp.second];
            unit(tmp.first,tmp.second);
        }
    }

    cout<<ans<<endl;

    return 0;
}