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++: #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;
}

C++: #include<iostream>
using namespace std;
static const int MAX=100;
static const int INFTY=2000000000;
static const int WHITE=0;
static const int GRAY=1;
static const int BLACK=2;

int n,M[MAX+1][MAX+1];
int prim(){
    int u,minv;
    int d[MAX+1],p[MAX+1],color[MAX+1];
    for(int i=1;i<=n;i++){
        d[i]=INFTY;
        p[i]=-1;
        color[i]=WHITE;
    }
    d[1]=0;
    while(1){
        minv=INFTY;
        u=-1;
        for(int i=1;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=1;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=1;i<=n;i++){
        if(p[i]!=-1) sum+=M[i][p[i]];
    }
    return sum;
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        for(int j=1;j<=n;j++){
            int e;
            cin>>e;
            M[i][j]=(e==-1)?INFTY:e;
        }
    }
    cout<<prim()<<"\n";
    return 0;
}

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

int m,n,x,ans;
int P[100+10],edge1[2000+10],edge2[2000+10];


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

bool same(int a, int b){
	return root(a)==root(b);
}
	
void unite(int a, int b){
	P[root(a)] = root(b);
}

int main() {
	pair<int,int> edges[2000+10];
	cin >> n;
	
	for (int i=1; i<=n; i++){
		P[i] = i;
	}
	
	m = 0;
	for (int i=1; i<=n; i++){
		for (int j=1; j<=n; j++){
			cin >> x;
			if (x>-1){
				edge1[m] = i;
				edge2[m] = j;
				edges[m] = make_pair(x, m);
				m+=1;
			}
		}
	}
	
	sort(edges, edges+m);
	n=1;
	for (int i=0; i<m; i++){
		if (n>=m) break;
		if (!same(edge1[edges[i].second], edge2[edges[i].second])){
			unite(edge1[edges[i].second], edge2[edges[i].second]);
			ans += edges[i].first;
			n+=1;
		}
	}
	
	cout << ans << endl;
	
}