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 <vector>
#include <utility>
#include <queue>

using namespace std;
 
int prim(vector<vector<pair<int, int> > >& G) {
	int cost = 0;
	const int N = G.size();
	vector<bool> used(G.size());
	priority_queue<pair<int, int>, vector<pair<int, int> >, greater<pair<int, int> > > pq;
	pq.push(make_pair(0, 0));
	while (!pq.empty()) {
		pair<int, int> p = pq.top(); pq.pop();
		int now = p.second;
		if (used[now]) continue;
		used[now] = true;
		cost += p.first;
		for (auto e : G[now])
			pq.push(make_pair(e.second, e.first));
	}
	return cost;
}

int main() {
	int n; cin >> n;
	vector<vector<pair<int, int> > > G(n);
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			int a; cin >> a;
			if (a != -1) G[i].push_back(make_pair(j, a));
		}
	}
	cout << prim(G) << endl;

	return 0;
}

C++: #include <iostream>
#include <string>
#include <cstring>
#include <fstream>
#include <cmath>
#include <iomanip>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <map>
#include <deque>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <list>
#include <unordered_map>

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(true){
        minv = INFTY;
        u = -1;
        for (int i=0;i<n;i++){
            if (minv > d[i] and 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 and 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;

}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
//#include "MyMath.h"
//#include "MyDisjointset.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <functional>
#include <stdio.h>
using namespace std;
typedef pair<int, int> P;
const int INF = 2000000000;
int main() {
	int n; cin >> n;
	int m[101][101];
	for (int i = 0; i < n; i++)for (int j = 0; j < n; j++)
		cin >> m[i][j];
	int res = 0;
	int *d = new int[n];
	fill(d, d + n, INF); 
	d[0] = 0;
	bool *visit = new bool [n];
	priority_queue <P, vector<P>, greater<P> > q;
	q.push(P(d[0], 0));
	while (!q.empty()) {
		int f = q.top().first, s = q.top().second;
		visit[s] = true;
		res += f;
		q.pop();
		for (int i = 0; i < n; i++)
			if (!visit[i] && m[s][i] != -1 && d[i] > d[s] + m[s][i]) {
				d[i] = d[s] + m[s][i];
				q.push(P(d[i], i));
			}
	}
	cout << res << endl;
	delete[] d, visit;
	return 0;
}

C++: #include <bits/stdc++.h>
#define r(i,a,n) for(int i=a;i<n;i++)
using namespace std;
int main(){
	int n,p;
	while(cin>>n>>p,n){
		int q,a[10000][1261],ch[10000][1261],b,c,d,e;
		r(i,0,p)r(j,0,1261)ch[i][j]=a[i][j]=0;
		cin>>q;
		r(i,0,q){
			cin>>b>>c>>d>>e;
			if(e==1){a[d-1][b]++;ch[d-1][b]=c;}
			else{
				for(int j=b-1;j>=0;j--){
					if(ch[d-1][j]==c)break;
					a[d-1][j]++;
				}
			}
		}
		cin>>q;
		while(q--){
			int s=0;
			cin>>b>>c>>d;
			r(i,b,c)if(a[d-1][i])s++;
			cout<<s<<endl;
		}
	}
}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll INF = 1e18;
const int inf = 1e9;
#define rep(i, n) for (int i = 0; i < n; i++)
using Graph = vector<vector<int>>;
using pint = pair<int, int>;
int dx[4] = {1, 0, -1, 0}, dy[4] = {0, 1, 0, -1};
int dxx[8] = {1, 1, 1, 0, 0, -1, -1, -1}, dyy[8] = {-1, 0, 1, -1, 1, -1, 0, 1};

int n;
const int MAX = 100;
int g[MAX][MAX];

int prim() {
    int u, minv;
    int d[MAX], p[MAX];
    bool seen[MAX] = {};
    rep (i, n) {
        d[i] = inf;
        p[i] = -1;
    }
    d[0] = 0;
    while (1) {
        minv = inf;
        u = -1;
        rep (v, n) {
            if (!seen[v] && minv > d[v]) {
                u = v;
                minv = d[v];
            }
        }
        if (u == -1) break;
        seen[u] = 1;
        rep (i, n) {
            if (!seen[i] && g[u][i] != -1) {
                if (d[i] > g[u][i]) {
                    d[i] = g[u][i];
                    p[i] = u;
                }
            }
        }
    }
    int sum = 0;
    rep (i, n) sum += d[i];
    // rep (i, n) cout << d[i] << " ";
    return sum;
}

int main() {
    cin >> n;
    rep (i, n) rep (j, n) cin >> g[i][j];
    // cout << prim << "\n";
    cout << prim() << "\n";
}