Go: package main

import (
	"bufio"
	"fmt"
	"log"
	"math"
	"os"
	"strconv"
	"strings"
)

type color int

const (
	white color = iota // 未訪問
	mst                // MSTとして確定
)

// 頂点
type node struct {
	matrix   []int // 隣接行列
	minToMst int   // MSTへの重み最小値
	parent   int   // 最小値の相手
	color    color
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	n := eGetInt(scanner)

	nodes := make([]node, n)
	for i := 0; i < n; i++ {
		nodes[i].matrix = eAtoi((strings.Fields(eGetline(scanner))))
		nodes[i].parent = -1
		nodes[i].minToMst = math.MaxInt16
		nodes[i].color = white
	}

	// 初回はnode[0]がMSTに入るように,minToMstを設定
	nodes[0].minToMst = 0
	for { // 全部チェックするまで

		// どの頂点を新たにMSTに取り込むか
		min := math.MaxInt16
		u := -1
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].minToMst < min {
				u = i
				min = nodes[i].minToMst
			}
		}

		if u == -1 {
			break
		}
		// MSTに追加する頂点決定
		nodes[u].color = mst

		// MSTに属していない頂点それぞれについて,MSTとの最小の重みを更新
		for i := 0; i < n; i++ {
			if nodes[i].color == mst {
				continue
			}
			if nodes[i].matrix[u] == -1 {
				// 接してない
				continue
			}
			if nodes[i].matrix[u] < nodes[i].minToMst {
				// node[u]との重みが最小
				nodes[i].minToMst = nodes[i].matrix[u]
				nodes[i].parent = u
			}
		}
	}

	sum := 0
	for _, v := range nodes {
		// node[0]はparentが入っていない
		if v.parent != -1 {
			sum += v.matrix[v.parent]
		}
	}
	fmt.Println(sum)
}

func eGetInt(scanner *bufio.Scanner) int {
	t := eAtoi(strings.Fields(eGetline(scanner)))
	return t[0]
}

func eGetline(p *bufio.Scanner) string {
	if !p.Scan() {
		if err := p.Err(); err != nil {
			log.Fatal(err.Error())
		}
		return ""
	}
	return p.Text()
}

func eAtoi(s []string) []int {
	ints := make([]int, len(s))
	var err error
	for i, e := range s {
		ints[i], err = strconv.Atoi(e)
		if err != nil {
			log.Fatal(err.Error())
		}
	}
	return ints
}

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

const int white = 0;
const int gray = 1;
const int black = 2;
const int Max_n = 100;
const int Infty = (1 << 21);

int M[Max_n][Max_n];
int n;

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

    d[0] = 0;

    while(1){
        minv = Infty;
        u = -1;
        for(int i=0; i<n; i++){
            if(color[i] != black && d[i] < minv){
                minv = d[i];
                u = i;
            }
        }
        if(u == -1){
            break;
        }

        color[u] = black;

        for(int v=0; v<n; v++){
            if(color[v] != black && M[u][v] != Infty){
                if(M[u][v] < d[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++: #include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#define maxn 101
#define Max 10000 
using namespace std;
int n,ans=0;
int map[maxn][maxn];

//struct edge
//{
//	int u;
//	int w;
//	edge(int u=0,int w=Max):u(u),w(w){}
//	bool operator <???(const node& rhs) const
//	{
//		return w>rhs.w;
//	} 
//};

void prim()
{
	int d[maxn];
	bool vis[maxn];
	memset(vis,0,sizeof(vis));
	for(int i=1;i<=n;++i)
	{
		d[i]=Max;
		vis[i]=0;
	}
	d[1]=0;
	while(1)
	{
		int MIN=Max;
		int u=-1;
		for(int i=1;i<=n;++i)
			if(MIN>d[i]&&!vis[i])
			{
				MIN=d[i];
				u=i;
			}
		if(u==-1) break;
		vis[u]=1;
		ans+=d[u];
		for(int i=1;i<=n;++i)
		{
			if(!vis[i] && map[u][i]!=Max)
			  if(d[i]>map[u][i])
			  	d[i]=map[u][i];
		}
	}
	return;
}

int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;++i)
	  for(int j=1;j<=n;++j)
	  {
	  	int x;
	  	scanf("%d",&x);
	  	if(x!=-1)
	  	  map[i][j]=x;
	  	else
	  	  map[i][j]=Max;
	  }
	prim();
	printf("%d\n",ans);
	return 0;
}

C++: // AOJ ALDS 1_12_A
#include<cstdio>
#include<algorithm>
#include<vector>
#define rep(i,a) for( int i = 0; i != (a); ++i )

struct edge
{
	int from, to, cost;

	edge( int from, int to, int cost )
	:	from( from ), to( to ), cost( cost )
	{}
};

int n;
std::vector<edge> es;

int par[100], rank[100];

void init()
{
	rep( i, n )
		par[i] = i, rank[i] = 0;

	return;
}

int find( int x )
{
	if( x == par[x] )
		return x;
	else
		return par[x] = find( par[x] );
}

void unite( int x, int y )
{
	x = find( x );
	y = find( y );
	if( x == y )
		return;

	if( rank[x] < rank[y] )
		par[x] = y;
	else
	{
		par[y] = x;
		if( rank[x] == rank[y] )
			++rank[x];
	}

	return;
}

bool same( int x, int y )
{
	return find( x ) == find( y );
}

int main()
{
	scanf( "%d", &n );
	rep( i, n )
	{
		rep( j, n )
		{
			int a;
			scanf( "%d", &a );
			if( ~a )
				es.push_back( edge( i, j, a ) );
		}
	}

	std::sort( es.begin(), es.end(), []( const edge& e1, const edge& e2 ){ return e1.cost < e2.cost; } );

	init();

	int ans = 0;
	rep( i, es.size() )
	{
		if( !same( es[i].from, es[i].to ) )
		{
			ans += es[i].cost;
			unite( es[i].from, es[i].to );
		}
	}

	printf( "%d\n", ans );

	return 0;
}

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

void print(const vector<int> &v) {
    cout << v[0];
    for (int i = 1, size = v.size(); i < size; i++) {
        cout << " " << v[i];
    }
    cout << endl;
}

int main() {
    int n;
    while (cin >> n) {
        vector<int> a(n);
        for (int i = 0; i < n; i++) {
            cin >> a[i];
        }
        print(a);
        for (int j = 1; j < n; j++) {
            int key = a[j];
            int i = j - 1;
            while (0 <= i && key < a[i]) {
                a[i + 1] = a[i];
                i--;
            }
            a[i + 1] = key;
            print(a);
        }
    }
}

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, minv;
  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) {
    minv = INFTY;
    u = -1;
    for (int i = 0; i < n; i ++) {
      if (minv > d[i] && color[i] != BLACK) {
        u = i;
        minv = 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;
}