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;
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;

struct Node{
  int color, dist, parent;
};

int n, M[MAX][MAX];
Node node[MAX];

void Printnodes(){
  string col[3] = {"WHITE", "GRAY ", "BLACK"};
  for(int i = 0; i < n; i++){
    cout << "nodeID : " << i ;
    cout << " color : " << col[node[i].color];
    cout << " parent : " << node[i].parent;
    cout << " dist : " << node[i].dist << endl;
  }
  cout << endl;
}

int main(){
  cin >> n;

  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> M[i][j];
    }
    node[i].color = WHITE;
    node[i].dist = INFTY;
    node[i].parent = -1;
  }

  int p = 0, totaldist = 0;;
  node[p].color = BLACK;
  node[p].dist = 0;

  while(true){
    //Printnodes();

    for(int i = 0; i < n; i++){
      if(M[p][i] > 0 && node[i].color != BLACK){
        node[i].dist = node[p].dist + M[p][i];
        node[i].parent = p;
        node[i].color = GRAY;
      }
    }

    int min_d = INFTY;
    p = -1;
    for(int i = 0; i < n; i++){
      if(node[i].dist < min_d && node[i].color != BLACK){
        min_d = node[i].dist;
        p = i;
      }
    }

    if(p == -1)
      break;

    node[p].color = BLACK;
    totaldist = node[p].dist;
    //cout << "node " << p << " turns to BLACK!" << endl;
    //cout << "Total distance is " << totaldist << endl;
  }

  cout << totaldist << endl;
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <queue>

using namespace std;

using vi = vector<int>;
using vvi = vector<vi>;
using pii = pair<int, int>;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define IN(v) int v;cin>>v;
#define OUT(v) cout<<v<<endl

int main() {
  IN(N);

  vvi A(N, vi(N, -1));
  REP(i, N) {
    REP(j, N) {
      IN(a);
      A[i][j] = a;
    }
  }
  priority_queue<pii, vector<pii>, greater<pii>> edge;
  REP(i, N) {
    if (A[0][i] != -1)
      edge.push(make_pair(A[0][i], i));
  }
  vector<bool> visited(N, false);
  visited[0] = true;
  int ans = 0;
  while (!edge.empty()) {
    pii p = edge.top(); edge.pop();
    if (visited[p.second])
      continue;
    visited[p.second] = true;
    ans += p.first;
    REP(i, N) {
      if (A[p.second][i] != -1 && !visited[i])
        edge.push(make_pair(A[p.second][i], i));
    }
  }
  OUT(ans);

  return 0;
}

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

static const int MAX=100;
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;

int n,M[MAX][MAX];

int prime(){
  int u,mincost;
  int d[MAX],p[MAX],color[MAX];

  for(int i=0;i<n;i++){
    d[i]=INT_MAX;
    p[i]=-1;
    color[i]=WHITE;
  }

  d[0]=0;

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

    for(int i=0;i<n;i++){
      if(color[i]!=BLACK&&M[u][i]!=INT_MAX){
	if(M[u][i]<d[i]){
	  d[i]=M[u][i];
	  p[i]=u;
	  color[i]=GRAY;
	}
      }
    }
  }

  int sum=0;
  for(int i=0;i<n;i++) sum+=d[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;
      if(e==-1) M[i][j]=INT_MAX;
      else M[i][j]=e;
    }
  }
  cout<<prime()<<endl; 
  return 0;
}

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

using namespace std;

/* UnionFind：素集合系管理の構造体(union by rank)
	isSame(x, y): x と y が同じ集合にいるか。 計算量はならし O(α(n))
	unite(x, y): x と y を同じ集合にする。計算量はならし O(α(n))
*/
struct UnionFind {  // The range of node number is u 0 v n-1
	vector<int> rank, parents;
	UnionFind() {}
	UnionFind(int n) {  // make n trees.
		rank.resize(n, 0);
		parents.resize(n, 0);
		for (int i = 0; i < n; i++) {
			makeTree(i);
		}
	}
	void makeTree(int x) {
		parents[x] = x;  // the parent of x is x
		rank[x] = 0;
	}
	bool isSame(int x, int y) { return findRoot(x) == findRoot(y); }
	void unite(int x, int y) {
		x = findRoot(x);
		y = findRoot(y);
		if (rank[x] > rank[y]) {
			parents[y] = x;
		}
		else {
			parents[x] = y;
			if (rank[x] == rank[y]) {
				rank[y]++;
			}
		}
	}
	int findRoot(int x) {
		if (x != parents[x]) parents[x] = findRoot(parents[x]);
		return parents[x];
	}
};

// 辺の定義
struct Edge {
	long long u;
	long long v;
	long long cost;
};

bool comp_e(const Edge &e1, const Edge &e2) { return e1.cost < e2.cost; } // 辺を直接比較するための関数

/* Kruskal :クラスカル法で minimum spanning tree を求める構造体
	入力: 辺のvector, 頂点数V
	最小全域木の重みの総和: sum
	計算量: O(|E|log|V|)
*/

struct Kruskal {
	UnionFind uft;
	long long sum;  // 最小全域木の重みの総和
	vector<Edge> edges;
	int V;
	Kruskal(const vector<Edge> &edges_, int V_) : edges(edges_), V(V_) { init(); }
	void init() {
		sort(edges.begin(), edges.end(), comp_e); // 辺の重みでソート
		uft = UnionFind(V);
		sum = 0;
		for (auto e : edges) {
			if (!uft.isSame(e.u, e.v)) { // 閉路にならなければ加える
				uft.unite(e.u, e.v);
				sum += e.cost;
			}
		}
	}
};

int main() {

	int n;
	cin >> n;
	vector<vector<int>> VE(n, vector<int>(n));
	int counter=0;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> VE[i][j];
			if (VE[i][j] != -1) { counter++; }
		}
	}

	int V, E;
	V = n;
	E = counter;
//	cin >> V >> E;
	vector<Edge> edges(E);
//	for (int i = 0; i < E; i++) {
	counter = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			long long s, t, w;
			//		cin >> s >> t >> w;
			if (VE[i][j] != -1) {
				s = i;
				t = j;
				w = VE[i][j];

				Edge e = { s, t, w };
				edges[counter] = e;
				counter++;
			}
		}
	}
//	}


	Kruskal krs(edges, V);
	cout << krs.sum << endl;
	return 0;
}