Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] > 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A > edges[j].A })

	sum := 0
	for len(edges) > 0 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

C++: //compiledef
#include <bits/stdc++.h>
#define rep(i, n)for(i=0;i<(n);i++)
#define per(i, n) for(i=(n);i>0;i--)
#define repx(i, n, x) for(i=(x);i<(n);i++)
#define xper(i, n, x) for(i=(n);i>(x);i--)
#define pback push_back

//c++def
using namespace std;
typedef long long int ll;
const long long int MOD = 1e9+7;
const long long int MOD2 = 998244353;
int w[200][200];
int prim_mst(int n){
	int i;
	int j;
	int cost = 0;
	int d[200];
	int pi[200];
	int color[200];
	rep(i, n){
		d[i]= 2e9;
		pi[i]=-1;
		color[i] = 0;
	}
	d[0] = 0;
	while(29091101){
		int mincost = 2e9;
		rep(i, n){
			if(color[i] != 2 && d[i] < mincost){
				mincost = d[i];
				j = i;
			}
		}
		if(mincost == 2e9)break;
		color[j] = 2;
		for(int v=0; v<n;v++){
			if(color[v] != 2 && w[j][v] < d[v]){
				pi[v] = j;
				d[v] = w[j][v];
			}
		}
	}
	rep(i, n){
		if(pi[i] != -1) cost += w[i][pi[i]];
	}
	return cost;
}

int main(){
	int n;
	int i, j;
	int tmp;
	cin >> n;
	rep(i, n){
		rep(j, n){
			cin >> tmp;
			if(tmp == -1) w[i][j] = 2e9;
			else w[i][j] = tmp;
		}
	}
	cout << prim_mst(n) << endl;
}

C++: //kruskal tree
#include <iostream>
#include <algorithm>
using namespace std;
#define M 999
int parent[M],a[M],b[M];
pair<int,int>node[M];
int root(int a){return parent[a]==a?a:parent[a]=root(parent[a]);}
int unite(int a,int b){
	int x=root(a),y=root(b);
	if(x==y)return 0;
	parent[x]=y;
	return 1;
}
int main(){
	int i,j,s,n,m,x;
	cin>>n;
		for(m=i=0;i<n;i++)for(j=0;j<n;j++)if(cin>>x,~x)a[m]=i,b[m]=j,node[m].first=x,node[m].second=m++;
		sort(node,node+m);
		for(i=0;i<n;i++)parent[i]=i;
		for(s=i=0;i<m;i++)if(unite(a[node[i].second],b[node[i].second]))s+=node[i].first;
	cout<<s<<endl;
}

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<cstdio>
#include<functional>
#include<algorithm>
#define F first
#define SF second.first
#define SS second.second
using namespace std;
typedef pair<int,int> P;
typedef pair<int,P> P2;
int main(void)
{
	int i,j,n,a,par[100],leng[100],sum,p1,cnt,s,t;
	P2 pp[100*99/2];
	scanf("%d",&n);
	p1=0;
	for(i=0;i<n;i++)	{
		for(j=0;j<n;j++)	{
			scanf("%d",&a);
			if(i<j && a!=-1)	{
				pp[p1].F=a;
				pp[p1].SF=i;
				pp[p1].SS=j;
				p1++;
			}
		}
	}
	sort(pp,pp+p1);
	for(i=0;i<n;i++)	{
		leng[i]=1;	par[i]=i;
	}
	cnt=1;	sum=0;
	for(i=0;i<p1;i++)	{
		s=pp[i].SF;	t=pp[i].SS;
		while(par[s]!=s)	s=par[s];
		while(par[t]!=t)	t=par[t];
		if(s!=t)	{
			if(leng[s]>leng[t])	par[t]=s;
			else if(leng[s]<leng[t])	par[s]=t;
			else {
				par[s]=t;	leng[t]++;

			}
			sum+=pp[i].F;
			cnt++;
			if(cnt==n)	break;
		}
	}
	printf("%d\n",sum);
	return 0;
}

C++: #include<iostream>
using namespace std;
static const int whi=0;
static const int gra=1;
static const int bla=2;
static const int MAXX=(1<<21);
int color[110];
int a[110][110];
int minni[110];
int parent[110];
int n;

int prim(){
  int b=0;
  int minmin=0;
  int result=0;
  for(int i=0;i<n;i++){
    color[i]=whi;
    minni[i]=MAXX;
    parent[i]=-1;
  }
  minni[0]=0;
  while(1){
    minmin=MAXX;
    b=-1;
    for(int i=0;i<n;i++){
      if(color[i]!=bla&&minni[i]<minmin){
	b=i;
	minmin=minni[i];
	
      }
    }
    if(b==-1){
      break;
    }
    color[b]=bla;
    for(int j=0;j<n;j++){
      if(color[j]!=bla&&a[b][j]!=MAXX){
	if(a[b][j]<minni[j]){
	  minni[j]=a[b][j];
	  parent[j]=b;
	  color[j]=gra;
	}
      }
    }
  }
  for(int i=0;i<n;i++){
    if(parent[i]!=-1) result+=a[i][parent[i]];
  }
  return result;
}

int main(){
  cin>>n;

  int s;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++){
      cin>>s;
      a[i][j]=(s==-1) ? MAXX : s;
    }
  }
  cout<<prim()<<endl;
}

C++: #include <bits/stdc++.h>
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,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(1){
    min=INFTY;
    u=-1;
    for(int i=0;i<n;i++){
      if(min>d[i] && color[i]!=BLACK){
        u=i;
        min=d[i];
      }
    }
    if(u==-1) break;
    color[u]=BLACK;
    for(int j=0;j<n;j++){
      if(color[j]!=BLACK && m[u][j]!=INFTY){
        if(d[j]>m[u][j]){
          d[j]=m[u][j];
          p[j]=u;
          color[j]=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;
}