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 <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
//#define ll long long
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
#define rep(i, n) REP(i, 0, n)
#define rep_rev(i, n) for (int (i) = (int)(n) - 1 ; (i) >= 0 ; --(i))
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for(int i = x; i < n; i++)
#define all(x) (x).begin(),(x).end()
ll t1,t2,t3;
const ll mod = 1000000007;
const int INF = 1e9;
const ll INFLONG = 1e18;

int main(){
  ll n;
  cin >> n;
  vector<vector<ll>> vec(n,vector<ll>(n));
  rep(i,n){
    rep(j,n){
      cin >> vec[i][j];
    }
  }
  vector<ll> arr(n,0);
  arr[0] = 1;
  priority_queue<pair<ll,ll>> pq;
  rep(i,n){
    if(vec[0][i] != -1){
      pq.push(make_pair(-vec[0][i],i));
    }
  }
  pair<ll,ll> pa;
  ll ans = 0;
  while(!pq.empty()){
    pa = pq.top();
    pq.pop();
    if(arr[pa.second] == 0){
      arr[pa.second] = 1;
      ans -= pa.first;
      rep(i,n){
        if(vec[pa.second][i] != -1){
          pq.push(make_pair(-vec[pa.second][i],i));
        }
      }
    }
  }
  cout << ans << endl;
}

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

#define MAX (1<<21)

int n,M[101][101];
int vis[101],d[101],p[101];

int prim(){
    int u,minv,i,v,j;
    for( i = 0; i < n; i++ ){
        d[i] = MAX;
        p[i] = -1;
    }
    d[0] = 0;
    while(1){
        minv = MAX;
        u = -1;
        for( i = 0; i < n; i++ ){
            if( minv > d[i] && !vis[i] ){
                u = i;
                minv = d[i];
            }
        }
        if( u == -1 ) break;
        vis[u] = 1;
        for( v = 0; v < n; v++ ){
            if( !vis[v] && M[u][v] != MAX ){
                if( d[v] > M[u][v] ){
                    d[v] = M[u][v];
                    p[v] = u;
                }
            }
        }
    }
    int sum = 0;
    for( i = 0; i < n; i++ ){
        if( p[i] != -1 ) sum += M[i][p[i]];
    }
    return sum;
}


int main(){
    int i,j,k,m;
    cin >> n;
    for( i = 0; i < n; i++ ){
        for( j = 0; j < n; j++ ){
            cin >> k;
            M[i][j] = (k == -1) ? MAX : k;
        }
    }
    cout << prim() << endl;
}

C++: #include <map>
#include <set>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <string>
#include <vector>
#include <complex>
#include <cstdlib>
#include <cstring>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <functional>
  
#define mp       make_pair
#define pb       push_back
#define all(x)   (x).begin(),(x).end()
#define rep(i,n) for(int i=0;i<(n);i++)
  
using namespace std;
  
typedef    long long          ll;
typedef    unsigned long long ull;
typedef    vector<bool>       vb;
typedef    vector<int>        vi;
typedef    vector<vb>         vvb;
typedef    vector<vi>         vvi;
typedef    pair<int,int>      pii;
  
const int INF=1<<29;
const double EPS=1e-9;
  
const int dx[]={1,0,-1,0,1,1,-1,-1},dy[]={0,-1,0,1,1,-1,-1,1};

class UnionFind {
public:
    int N;
    std::vector<int> parent;
    UnionFind(int n) : N(n), parent(N, -1) {
    }
    void Union(int a, int b) {
        a = root(a);
        b = root(b);
        int sizea = size(a);
        int sizeb = size(b);
        if (sizea > sizeb) {
            int temp = a;
            a = b;
            b = temp;
        }
        parent[b] += parent[a];
        parent[a] = b;
    }
    int root(int a) {
        if (parent[a] < 0) return a;
        return parent[a] = root(parent[a]);
    }
    int size(int a) {
        return -parent[root(a)];
    }
    bool Find(int a, int b) {
        return root(a) == root(b);
    }
};

struct edge {
    int a;
    int b;
    int c;
    bool operator<(const edge &rhs) const {
        return c < rhs.c;
    }
    edge(int a_, int b_, int c_) : a(a_), b(b_), c(c_) {

    }
};

int main() {
    int N;
    cin >> N;

    UnionFind uf(N);
    std::vector<edge> e;
    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            int c;
            cin >> c;
            if (c == -1) continue;
            e.push_back((edge){i, j, c});
        }
    }

    sort(e.begin(), e.end());

    int ans = 0;
    for (int i = 0; i < e.size(); i++) {
        if (!uf.Find(e[i].a, e[i].b)) {
            uf.Union(e[i].a, e[i].b);
            ans += e[i].c;
        }
    }
    cout << ans << endl;
    return 0;
}

C++: #include<iostream>
#include<climits>
#include<vector>
#include<list>
#include<functional>
#include<algorithm>
#include<string>
#include<cmath>
#include<complex>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<deque>
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) for(int i=0;i<(n);i++)
#define INF (int)1e9
#define INFL (ll)1e11
using namespace std;
typedef long long ll;
typedef pair<int, int> P;

int prim(vector<vector<int>> a) {
	int n = a.size();
	priority_queue<P, vector<P>, greater<P>> pq;
	pq.push(P(0, 0));
	set<int> mst;
	int res = 0;
	while (mst.size() < n) {
		int s = pq.top().second;
		res += pq.top().first;
		pq.pop();
		mst.insert(s);
		REP(j, n) {
			if (a[s][j] >= 0 && mst.find(j) == mst.end()) {
				pq.push(P(a[s][j], j));
			}
		}
	}
	return res;
}

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int n;
	cin >> n;
	vector<vector<int>> a(n, vector<int>(n));
	REP(i, n)REP(j, n) cin >> a[i][j];

	cout << prim(a) << "\n";
	
	return 0;
}