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>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>

using namespace std;

#define MAX_N 100

int G[MAX_N][MAX_N];

int mincost[MAX_N];
bool used[MAX_N];
int V;
int prim() {
	for (int i = 0; i < V; i++) {
		mincost[i] = INT_MAX;
		used[i] = false;
	}
	mincost[0] = 0;
	int res = 0;

	while (1) {
		int v = -1;
		for (int u = 0; u < V; u++)
			if (!used[u] && (v == -1 || mincost[u] < mincost[v]) )
				v = u;

		if (v == -1)
			break;
		used[v] = true;
		res += mincost[v];

		for (int u = 0; u < V; u++)
			mincost[u] = min(mincost[u], G[v][u]);
	}
	return res;
}

int main() {
	int n, c;
	cin >> n;
	V = n;
	for (int i = 0; i < n; i++)
		for (int j = 0; j < n; j++) {
			cin >> c;
			if (c == -1) c = INT_MAX;
			G[i][j] = c;
		}

	cout << prim() << endl;
	return 0;
}

C++: #include<bits/stdc++.h>
#define REP(i,n) for(long long i=0;i<n;++i)
#define FOR(i,a,b) for(long long i=a;i<b;++i)
using namespace std;
const int MAX=100,INF=1<<30,WHI=0,GRA=1,BLA=2;
int n,m[MAX][MAX];
int prim(){
    int u,minv;
    int d[MAX],p[MAX],color[MAX];
    fill(d,d+n+1,INF);
    fill(p,p+n+1,-1);
    fill(color,color+n+1,WHI);
    d[0]=0;
    while(1){
        minv=INF;
        u=-1;
        REP(i,n){
            if(minv>d[i]&&color[i]!=BLA){
                u=i;
                minv=d[i];
            }
        }
        if(u==-1) break;
        color[u]=BLA;
        REP(v,n){
            if(color[v]!=BLA&&m[u][v]!=INF){
                if(m[u][v]<d[v]){
                    d[v]=m[u][v];
                    p[v]=u;
                    color[v]=GRA;
                }
            }
        }
    }
    int sum=0;
    REP(i,n){
        if(p[i]!=-1) sum+=m[i][p[i]];
    }
    return sum;
}
int main(){
    scanf("%d",&n);
    REP(i,n){
        REP(j,n){
            int e;
            scanf("%d",&e);
            m[i][j]=(e==-1)?INF:e;
        }
    }
    printf("%d\n",prim());
    return 0;
}

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

typedef long long ll;


class Union_Find {
private:
    std::vector<int> par;
    std::vector<int> rank;

public:
    Union_Find(int n) { // ?????????: O(n)
	par = rank = std::vector<int>(n);
	for(int i=0; i<n; i++) {
	    par[i]  = i;
	    rank[0] = 0;
	}
    }

    int root(int x) { // ??¨??????????±???????: O(?±(n)) 
	if(par[x] == x) return x;
	return par[x] = root(par[x]); // ??????????????????????????????????????????
    }

    void unite(int x, int y) { // x,y????????????????????????: O(?±(n)) 
	x = root(x); y = root(y);
	if( x == y ) return;

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

    bool same(int x, int y) { //x,y??????????????????????????????????????????: O(?±(n)) 
	return root(x) == root(y);
    }
};

struct Edge {
    ll s,t;
    ll w;
    bool operator < (const Edge& tgt) const {
	return w > tgt.w;
    }
};

ll Kruskal(priority_queue<Edge>& edges, const int V) {

    ll res = 0;
    
    Union_Find uf(V);
    while( !edges.empty() ) {
	Edge e = edges.top(); edges.pop();
	if( !uf.same(e.s, e.t) ) {
	    uf.unite(e.s, e.t);
	    res += e.w;
	}
    }
    return res;
}


int main () {

    ll V;
    cin >> V;

    priority_queue<Edge> edges;
    
    for(int i=0; i<V; i++) {
	for(int j=0; j<V; j++) {
	    ll d;
	    cin >> d;
	    if( d != -1 )
		edges.push( Edge{i,j,d} );
	}	
    }

    ll res = Kruskal(edges,V);
    cout << res << endl;    
    return 0;
}

C++: #include <bits/stdc++.h>
#define REP(i,n) for (int i = 0; i <(n); ++i)
#define REP2(i,x,n) for (int i = x; i <(n); ++i)
#define ALL(v) v.begin(), v.end()
#define RALL(v) v.rbegin(), v.rend()
using namespace std;
using ll = long long;
using P = pair<int,int>;
static const double PI = acos(-1);
static const int INF = 1e9+7;

/*
  最小全域木

  重み付きグラフの最小全域木の辺の重みの総和を計算する．
  最小全域木とは？：グラフで，すべての頂点に到達できるものの中で，　辺の重みが最小のもの
  プリムのアルゴリズム

*/

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];
  //d: MSTに属する頂点とそれ以外の頂点の中で，重みが最小の辺の重み
  //p: p[v]  MSTにおける頂点vの親
  //color 訪問状態

  //初期化
  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;

  //入力
  REP(i,n)REP(j,n){
    int e;
    cin >> e;
    if(e == -1) M[i][j] = INFTY;
    else M[i][j] = e;
  }

  cout << prim() << endl;

  return 0;
}