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>

using namespace std;
int n;
int dat[100][100];
int cost[100];
int done[100];

void prim(){
	for(int i=0;i<n;i++){
		cost[i]=1<<21;
		done[i]=0;
	}
	int s=0;	
	int next, ncost=1<<21;
	done[s]=1;
	cost[s]=0;
	int cnt=0;
	while(1){
		cnt++;
		if(cnt>20)
			return;
		
		ncost=1<<21;
		for(int j=0;j<n;j++){
			if(done[j]){
				for(int i=0;i<n;i++){
					if(dat[j][i]!=-1){
						if(cost[i]>=dat[j][i]){
							cost[i]=dat[j][i];
						}
						if(ncost>cost[i]&&!done[i]){
							next=i;
							ncost=cost[i];
						}
					}
				}
			}
		}
//		cout<<"next:"<<next<<" cost:"<<cost[next]<<endl;
		done[next]=1;
		int flag=true;
		for(int i=0;i<n;i++){
			if(!done[i]) flag = false;
		}
		if(flag)
			return;
	}
}

int main(){
	cin>>n;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin>>dat[i][j];
		}
	}
	prim();
	int sum=0;
	for(int i=0;i<n;i++){
		sum+=cost[i];
	}
	cout<<sum<<endl;
	return 0;
}

C++: 
#include<bits/stdc++.h>

using namespace std;

const int maxn=1e2+5;
const int inf=(1<<21);
const int white=0;
const int gray=1;
const int black=2;

int n,m[maxn][maxn];

int prim()
{
    int u,minv,sum=0;
    int d[maxn],p[maxn],color[maxn];
    for(int i=0;i<n;i++){
        d[i]=inf;
        color[maxn]=white;
        p[i]=-1;
    }
    d[0]=0;
    while(1){
        minv=inf;
        u=-1;
        for(int i=0;i<n;i++){
            if(minv<d[i]&&color[i]==white){
                minv=d[i];
                u=i;
            }
        }
        if(u==-1){
            break;
        }
        color[u]=black;
        sum+=d[u];
        for(int i=0;i<n;i++){
            if(color[i]!=black&&d[i]<m[u][i]){
                d[i]=m[u][i];
                p[i]=u;
                color[i]=gray;
            }
        }
    }
}

int main()
{
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            int e;
            cin>>e;
            m[i][j]=(e==-1)?inf:e;
        }
    }
    cout<<prim()<<endl;
    return 0;
}
/*
5
-1 2 3 1 -1
2 -1 -1 4 -1
3 -1 -1 1 1
1 4 1 -1 3
-1 -1 1 3 -1
*/

C++: #include <iostream>
#include <vector>
#include <algorithm>
#include <utility>
using namespace std;
int P[1010];
int cost[5000];
int src[5000];	
int dst[5000];
int A[100 + 10][100 + 10];
int M = 0;
vector<pair<int,int>> edges;

void init(int N)
{
    for(int i = 1; i <= N; ++i)
    {
        P[i] = i;
    }
}
 
int root(int a)
{
    if(P[a] == a)
    {
        return a;
    }
    return (P[a] = root(P[a]));
}
 
bool is_same_set(int a, int b)
{
    return root(a) == root(b);
}
 
void unite(int a, int b)
{
    P[root(a)] = root(b);
}

int main()
{
	int n = 0;
	cin >> n; 
	for(int r = 0; r < n; ++r)
	{
		for(int c = 0; c < n; ++c)
		{
			cin >> A[r][c];
		}
	}
	for (int r = 0; r < n; ++r)
	{
		for(int c = r + 1; c < n; ++c)
		{
			if(A[r][c] > -1)
			{
				cost[M] = A[r][c];
				src[M] = r;
				dst[M] = c;
				edges.push_back(make_pair(cost[M],M));
				M += 1;
			}
		}
	}
	sort(edges.begin(),edges.end());
	int sum = 0;
	init(n);
	for(int i = 0; i < M; ++i)
	{
		if(is_same_set(src[edges[i].second], dst[edges[i].second]) == 1) continue;
			unite(dst[edges[i].second],src[edges[i].second]);
			sum += edges[i].first;
	}
	cout << sum << endl;
}

C++: #include <iostream>
#include <queue>

using ll = long long;
using namespace std;
int n, p, A[100][100];
int d[100], P[100], c[100];
/* initialize */

int bfs(){
    int u, minv;
    int sum;
    for (int i = 0; i < n; ++i) {
        d[i] = 1<<30;
        P[i] = -1;
        c[i] = 0;
    }
    d[0] = 0;
    
    while(true) {
        minv = 1 << 30;
        u = -1;
        for (int i = 0; i < n; ++i) {
            if (minv > d[i] && c[i] != 2) {
                u = i;
                minv = d[i];
            }
        }
        if (u == -1)break;
        c[u] = 2;
        for (int j = 0; j < n; ++j) {
            if (c[j] != 2 && A[u][j] != 1 << 30) {
                if (d[j] > A[u][j]) {
                    d[j] = A[u][j];
                    P[j] = u;
                    c[j] = 1;
                }
            }
        }
    }
        sum = 0;
        for (int i = 0; i < n; ++i) {
            if (P[i] != -1) sum += A[i][P[i]];
        }
    return sum;
}
/* main */
int main() {
    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            cin >> p;
            if (p == -1) A[i][j] = 1<<30;
            else A[i][j] = p;
        }
    }
    cout << bfs() << "\n";
}

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;
        color[u]=BLACK;
        for(int v=0;v<n;v++){
            if(color[v]!=BLACK&&M[u][v]!=INFTY){
                if(M[u][v]<d[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 b;cin>>b;
            M[i][j]=(b==-1)? INFTY:b;
        }
    }
    
    cout << prim() << endl;
    
    return 0;
}