Go: package main

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

//util
var sc = bufio.NewScanner(os.Stdin)

func nextStr() string {
	sc.Scan()
	return sc.Text()
}

func nextInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func printList(list []int) {
	n := len(list)
	buf := bufio.NewWriter(os.Stdout)
	for _, v := range list[0 : n-1] {
		buf.Write([]byte(fmt.Sprintf("%d ", v)))
	}
	buf.Write([]byte(fmt.Sprintf("%d\n", list[n-1])))
	buf.Flush()
}

func max(a, b int) int {
	if a > b {
		return a
	} else {
		return b
	}
}

func min(a, b int) int {
	if a > b {
		return b
	} else {
		return a
	}
}

//solve
const (
	MAX   = 100
	INFTY = (1 << 21)
	WHITE = 0
	GRAY  = 1
	BLACK = 2
)

//V: グラフの頂点全体の集合
//T: MSTに属する頂点の集合
var (
	n     int
	M     [MAX][MAX]int //重みを記録する隣接行列
	color [MAX]int
	p     [MAX]int //MSTにおける頂点の親を記録
	d     [MAX]int //Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを記録
)

func prim() int {
	var u, minv int
	//初期化
	for i := 0; i < n; i++ {
		d[i] = INFTY
		p[i] = -1
		color[i] = WHITE
	}

	d[0] = 0

	for {
		//頂点uを決めていく
		//つまり、Tに属する頂点と、V−Tに属する頂点を繋ぐ辺の中で、重みが最小のものを決める
		minv = INFTY
		u = -1
		for i := 0; i < n; i++ {
			//未訪問かつ、辺の重みが最小となるuを選ぶ
			if minv > d[i] && color[i] != BLACK {
				u = i
				minv = d[i]
			}
		}

		if u == -1 {
			break
		}

		color[u] = BLACK
		for v := 0; v < n; v++ {
			//未訪問かつ、辺が存在するとき
			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
				}
			}
		}
	}

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

func main() {
	sc.Split(bufio.ScanWords)
	n = nextInt()

	for i := 0; i < n; i++ {

		for j := 0; j < n; j++ {
			tmp := nextInt()
			if tmp == -1 {
				tmp = INFTY
			}
			M[i][j] = tmp
		}

	}

	fmt.Println(prim())

}

C++: #include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<map>
#include<string>
#include<algorithm>
#include<functional>
#define ll long long
#define inf  999999999
#define pa pair<int,int>

using namespace std;

int n,a[200][200]={0};
void prim(){
	int d[200]={0};
	priority_queue<pair<int,pa> >  PQ; 
	pair<int,pa> q;
	pa r;
	int wei=0;
	int u=0,z=0;
	d[0]=1;
	while(z!=n-1){
		for(int j=0;j<n;j++){
			if(a[u][j]<0) PQ.push(make_pair(a[u][j],make_pair(u,j)));
		}
	while(1){
		if(PQ.size()==0) {
		//	cout<<"dv"<<endl;
		break;
		}
		q=PQ.top();
		PQ.pop();
		r=q.second;
	//	cout<<"rsec"<<r.second<<endl;
		if(d[r.second]==0) break;
		
	}
	u=r.second;
//	cout<<"a" <<u<<endl;
	d[u]=1;
	wei=wei+q.first;
	z++;
//	cout<<q.first<<endl;
	}
	cout<<-wei<<endl;
}



int main(){
	// your code goes here
	int m;
	cin>>n;
	
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
		cin>>m;
		a[i][j]=-m;
		}
	}
	prim();

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;

#define inf 1e9+7
typedef long long ll;

int n;
vector<vector<int> > cost;

void solve(int s){
    vector<bool> flg(n,false);
    flg[s]=true;
    vector<int> vc;
    vc.push_back(s);


    int sum=0;
    int mi,next;
    while(1){
        mi=inf;
        next=-1;
        for(int i=0;i<vc.size();i++){
            for(int j=0;j<n;j++){
                if(flg[j]||cost[vc[i]][j]<0)continue;
                if(mi>cost[vc[i]][j]){
                    mi=cost[vc[i]][j];
                    next=j;
                }
            }
        }
        if(next==-1)break;
        else{
            sum+=mi;
            flg[next]=true;
            vc.push_back(next);
        }
    }
    cout << sum << endl;
}

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

    cin >> n;
    cost.resize(n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            int a;
            cin >> a;
            cost[i].push_back(a);

        }
    }

    solve(0);
    return 0;
}

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(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;
        }
        for (int v = 0; v != n; ++v)
        {
            if (M[u][v] != INFTY && color[v] != BLACK)
            {
                if (d[v] > M[u][v])
                {
                    d[v] = M[u][v];
                    color[v] = GRAY;
                    p[v] = u;
                }
            }
        }
        color[u] = BLACK;
    }
    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<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;
		int w = pq.top().first;
		pq.pop();
		if (mst.find(s) == mst.end()) res += w;
		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;
}

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

const int N = 100;
int n;
int A[N][N];
bool visit[N] = {0};
priority_queue< pair<int, int> > Q;

int main()
{
	cin >> n;
	for (int i=0; i<n; i++)
	{
		for (int j=0; j<n; j++)
		{
			cin >> A[i][j];
		}
	}

	int mcost = -INT_MAX;

	for (int i=0; i<n; i++)
	{
		Q.push(pair<int, int>(0,i));

		int cost = 0;

		while (Q.size())
		{
			pair<int, int> q = Q.top();
			Q.pop();
			int k = q.second;
			if (visit[k]) continue;
			cost += q.first;
			visit[k]=true;
			for(int j=0;j<n;j++)
			{
				int c = A[k][j];
				if (c <= 0) continue;
				if (visit[j]) continue;
				Q.push(pair<int, int>(-c,j));
			}
		}

		if (mcost < cost) mcost = cost;
	}

	cout << -mcost << endl;
		
	return 0;
}