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 <iostream>
using namespace std;

const static int MAX = 100;
const static int INFTY = (1<<21);
const static int WHITE = 0;
const static int GRAY = 1;
const static 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 work;
      cin >> work;
      M[i][j] = (work == -1) ? INFTY : work;
    }
  }

  cout << prim() << endl;


  return 0;
}

C++: #include <iostream>
#include <queue>
#define INF 200000
using namespace std;
typedef pair<int,int> P;
P a;
priority_queue< P,vector<P> ,greater<P> > pq;
int map[101][101];
bool decided[101];
int sum,n;
int node,count;
void check(){
	node=1;
	decided[node]=true;
	count=n-1;
	while(1){
		for(int i=1;i<=n;i++){
			if(map[node][i]!=-1&&!decided[i]){
				a=make_pair(map[node][i],i);
				pq.push(a);
			}
		}
		while(decided[pq.top().second])pq.pop();
		sum+=pq.top().first;
		node=pq.top().second;
		decided[node]=true;
		count--;
		if(count==0)break;
		pq.pop();
	}
}

int main(){
	cin >>n;
	for(int i=1;i<=n;i++){
		for(int j=1;j<=n;j++){
			cin >> map[i][j];
		}
	}
	sum=0;
	check();
	cout << sum<<endl;
}

C++: // 最小全域木
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<stack>
#include<algorithm>
#include<iostream>
#include<cmath>
#include<vector>

#include<queue>

using namespace std;

#define MAX_N 100
// 値の定義
const int INV = -1;
//const int EXIST = 1;
//const int NO_EXIST = 0;

// グラフ情報を保持する配列
int ary_graph[MAX_N + 1][MAX_N + 1];

// 辺の重みの最小値を保持する配列
// ( 頂点に入力される辺に対しての値 )
int ary_MinEdgeWeight[MAX_N + 1];

int n = 0;

void MinimumSpanningTree(int start_vertex);

int main(void)
{
    int sum = 0;

    for(int i = 0; i < MAX_N + 1; i++)
    {
    	ary_MinEdgeWeight[i] = INV;

        for(int j = 0; j < MAX_N + 1; j++)
        {
            // 配列の初期化
            ary_graph[i][j] = INV;
        }
    }

    cin >> n;

    for(int i = 0; i < n; i++)
    {
        for(int j = 0; j < n; j++)
        {
            // 隣接行列の設定
            cin >> ary_graph[i][j];
        }
    }

    // 頂点１から最小全域木を探索する
    MinimumSpanningTree(0);

    // 結果の表示
    for(int i = 0; i < n; i++)
    {
        sum += ary_MinEdgeWeight[i];
    }

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

    return 0;
}

// 辺の重みを設定する関数
// s      : 辺の開始頂点
// t      : 辺の終了頂点
// weight : 辺の重み
void set_weight(int s, int t, int weight)
{

    if( ary_MinEdgeWeight[t] == INV )
    {
        // 辺の重みの初期値の設定
        ary_MinEdgeWeight[t] = weight;
    }
    else
    {
        if( ary_MinEdgeWeight[t] > ary_graph[s][t] )
        {
            // 辺の最小値の設定
            ary_MinEdgeWeight[t] = ary_graph[s][t];
        }
    }

    return;
}

// 最小全域木を探索する関数
// start_vertex : 起点となる頂点のNo.
void MinimumSpanningTree(int start_vertex)
{

    queue<int> Q;

    // 開始点の情報の設定
    Q.push(start_vertex);
    ary_MinEdgeWeight[start_vertex] = 0;

    while( !Q.empty() )
    {
        // キューの先頭要素を取得して, 削除する
        int u = Q.front();
        Q.pop();

        for(int i = 0; i < n; i++)
        {
            // 隣接点を全て検索する
            int weight = ary_graph[u][i];

            if( weight != INV )
            {

                // 辺の重みを設定する
                set_weight(u, i, weight);
                //set_weight(i, u, weight);

                // キューにプッシュする
                Q.push(i);

                // 同じ辺を繰り返し辿らないように無効化する
                ary_graph[u][i] = INV;
                //ary_graph[i][u] = INV;
            }
        }
    }

    return;
}

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;
			}
		}
		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;
}