Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

type ElementKey int
type Node struct {
	key    ElementKey
	parent *Node
	rank   int
}

func newNode(key ElementKey) *Node {
	node := Node{}
	node.key = key
	node.parent = &node
	node.rank = 0

	return &node
}

func union(x, y *Node) {
	xSet := findSet(x)
	ySet := findSet(y)
	link(xSet, ySet)
}

func link(x, y *Node) {
	if x.rank > y.rank {
		y.parent = x
	} else {
		x.parent = y

		if x.rank == y.rank {
			y.rank++
		}
	}
}

func findSet(x *Node) *Node {
	if x != x.parent {
		x.parent = findSet(x.parent)
	}
	return x.parent
}

func newDisjointSets(nSets int) *DisjointSets {
	sets := DisjointSets{}
	sets.keyToNode = map[ElementKey]*Node{}
	for i := 0; i < nSets; i++ {
		key := ElementKey(i)
		sets.keyToNode[key] = newNode(key)
	}
	return &sets
}

type DisjointSets struct {
	keyToNode map[ElementKey]*Node
}

func (sets *DisjointSets) union(x, y ElementKey) {
	xNode := sets.keyToNode[x]
	yNode := sets.keyToNode[y]
	union(xNode, yNode)
}

func (sets DisjointSets) findSet(x ElementKey) *Node {
	xNode := sets.keyToNode[x]
	return findSet(xNode)
}

type Edge struct {
	i, j   int
	weight int
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	sets := newDisjointSets(n)
	edges := []Edge{}
	a := make([][]int, n)
	for i := 0; i < n; i++ {
		a[i] = make([]int, n)
		for j := 0; j < n; j++ {
			a[i][j] = nextInt()
			if a[i][j] >= 0 {
				e := Edge{
					i:      i,
					j:      j,
					weight: a[i][j],
				}
				edges = append(edges, e)
			}
		}
	}
	sort.Slice(edges, func(i, j int) bool { return edges[i].weight < edges[j].weight })
	totalWeight := 0
	for _, edge := range edges {
		i := ElementKey(edge.i)
		j := ElementKey(edge.j)
		if sets.findSet(i) != sets.findSet(j) {
			totalWeight += edge.weight
			sets.union(i, j)
		}
	}
	fmt.Println(totalWeight)
}

C++: #include <stdio.h>
#include <stdlib.h>
#include <iostream>
#define INF 1000000000
#define NUM 100
#define NIL -1
#define WHITE 0
#define BLACK 1
using namespace std;

int G[NUM][NUM];
int V[NUM];
int color[NUM];
int node_num;
int dist_sum = 0;

void init(){
    for(int i = 0; i < node_num; i++){
        for(int j = 0; j < node_num; j++){
            int a;
            scanf("%d", &a);
            if(a == -1){
                G[i][j] = INF;
            }else{
                G[i][j] = a;
            }
        }
    }

    for(int i = 0; i < node_num; i++){
        V[i] = INF;
        color[i] = WHITE;
    }
}

void updateAround(int n){
    color[n] = BLACK;
    for(int i = 0; i < node_num; i++){
        V[i] = min(V[i], G[n][i]);
    }

    int min_index = NIL;
    int min_value = INF;
    for(int i = 0; i < node_num; i++){
        if(color[i] == BLACK){
            continue;
        }
        if(V[i] < min_value){
            min_value = V[i];
            min_index = i;
        }
    }
    if(min_index != NIL){
        dist_sum += min_value;
        updateAround(min_index);
    }
}

int main(void){
    scanf("%d", &node_num);

    init();
    updateAround(0);

    printf("%d\n", dist_sum);
}

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 ( 1 ) {
		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;

	return 0;
}

C++: #include <iostream>
#include <stdio.h>
#include <vector>

#define inf 2001
using namespace std;

int main() {
	int n, tmp;
	int g[100][100];//与えられるグラフ
	bool used[100] = {}; //訪問済みを１、未訪問を０とする
	used[0] = 1;
	cin >> n;
	vector <int> x;

	//入力を受け取る
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			cin >> tmp;
			g[i][j] = tmp;
		}
	}
	x.push_back(0);
	int s, t, min, minn;
	int d[100] = {};
	while (x.size() != n) {
		min = inf;
		for (int i = 0; i < x.size(); ++i) {
			for (int j = 0; j < n; ++j) {
				if (!used[j] && g[x[i]][j] < min && g[x[i]][j] != -1) {//未訪問　かつ　最小値かつ　つながっている
					s = x[i];
					t = j;
					min = g[s][t];
				}
			}
		}
		x.push_back(t);
		used[t] = 1;
		d[t] = g[s][t];
	}
	int sum = 0;
	for (int i = 0; i < n; ++i) {
		sum += d[i];
	}
	cout << sum << endl;
}

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

int main(void)
{
	int n, now = 0, flag[101] = {};
	long ans = 0, an[100][100], min[100];

	cin >> n;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++)
			cin >> an[i][j];
		min[i] = 1000000000;
	}

	do {
		long key = LONG_MAX, key_i;
		flag[now] = 1;
		flag[100] = 0;

		for (int i = 0; i < n; i++) {
			if (an[now][i] != -1 && an[now][i] < min[i] && flag[i] == 0)
				min[i] = an[now][i];
			if (flag[i] == 0 && min[i] < key) {
				key = min[i];
				key_i = i;
			}
			if (flag[i] == 1)
				flag[100]++;
		}

		now = key_i;
		ans += key;

	} while (flag[100] != n - 1);

	cout << ans << endl;

	return 0;
}

C++: #include<stdio.h>

static const int MAX = 500;
static const int INFTY = (1<<21);

main(){
  int n, i, j, e, sum,M[MAX][MAX]={0};
  int u,minV,INT_MAX,A[MAX]={INFTY},key[MAX]={INFTY};
  /*

    your code


   */

  scanf("%d", &n);
  
  for ( i = 0; i< n; i++ ){
    for ( j = 0; j < n; j++ ){
      scanf("%d", &e);
      M[i][j] = (e==-1)?INFTY:e;
    }
  }
  
  
  while(1){
    minV = 
      for(i=1;i<=n;i++){
        if((i < minV) && 

  






















  sum = 0;

  for ( i = 0; i < n; i++ ){
    if ( p[i] != -1 ) sum += M[i][p[i]];
  }

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

  return 0;
}

C++: #include <algorithm>
#include <iostream>
#include <set>
#include <vector>
#define FOR(i,k,n) for (int (i)=(k); (i)<(n); ++(i))
#define REP(i,n) FOR(i,0,n)
#define pb push_back
#define mp make_pair
#define fst first
#define snd second
#define all(v) begin(v), end(v)
using namespace std;
typedef pair<int,int> PII;

int P[100]; //union_find

int root(int i){
    if(P[i] == i) return i;
    else return P[i] = root(P[i]);
}

bool same(int x, int y){
    return root(P[x]) == root(P[y]);
}

void unite(int x, int y){
    P[root(x)] = root(y);
}

int main(){
    int n;
    cin >> n;
    int g[n][n];
    vector<pair<int,PII>> V;
    REP(i,n){
        REP(j,n){
            cin >> g[i][j];
            if(i<j && g[i][j] >= 0) V.pb(mp(g[i][j],mp(i,j)));
        }
    }
    sort(all(V));
    REP(i,n){
        P[i] = i;
    }
    int wsum = 0, count = 0;
    REP(i,n*n){
        int x = V[i].snd.fst;
        int y = V[i].snd.snd;
        if(same(x,y)) continue;
        unite(x,y);
        wsum += V[i].fst;
        count++;
        if(count == n-1) break;
    }

    cout <<wsum<<endl;

    return 0;
}