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 <stdio.h>

#define MAX_N (105)
#define INF (10000)
int G[MAX_N][MAX_N];
int N;

int dist[MAX_N];
bool arrived[MAX_N];

int prim()
{
    int ret = 0;
    for ( int i = 0; i < N; i++ ) {
	arrived[i] = false;
	dist[i] = INF;
    }

    dist[0] = 0;

    while ( true ) {
	int min_dist = INF;
	int u = 0;
	for ( int i = 0; i < N; i++ ) {
	    if ( !arrived[i] && dist[i] < min_dist ) {
		min_dist = dist[i];
		u = i;
	    }
	}
	
	if ( min_dist == INF ) break;

	ret += dist[u];
	arrived[u] = true;

	for ( int i = 0; i < N; i++ ) {
	    if ( !arrived[i] && (G[u][i] != -1) && (dist[i] > G[u][i]) ) {
		dist[i] = G[u][i];
	    }
	}
    }

    return ret;
}

int main()
{
    int ans = 0;
    scanf("%d", &N);

    for ( int i = 0; i < N; i++ ) {
	for ( int j = 0; j < N; j++ ) {
	    scanf("%d", &G[i][j]);
	}
    }

    ans = prim();

    printf("%d\n", ans);

    return 0;
}

C++: #include<iostream>
#include<cstdio>
#define N 101
using namespace std;

int A[N][N];
int n;
int father[N];

int getparent(int i){
    while(father[i]!=i){
        i=father[i];
    }
    return i;
}
void mergeGroup(int a,int b){
    int fa=getparent(a);
    int fb=getparent(b);
    father[fb]=fa;
}

int prim(){
    int ans=0;
    int c=0;
    int minval=4000;
    int ab,ae;
    while(c<n-1){
        int b,e;
        minval=4000;
        for(b=0;b<n;b++){
            for(e=b+1;e<n;e++){
                if(A[b][e]!=-1 && A[b][e]<minval &&getparent(b)!=getparent(e)){
                    minval=A[b][e];
                    ab=b;
                    ae=e;
                    //printf("b= %d  e= %d \n",b,e);
                }
            }
        }
        ans+=A[ab][ae];
        //printf("ab= %d  ae= %d  mincost=%d \n ",ab,ae,minval);
        c++;
        mergeGroup(ab,ae);
    }
    return ans;
}

int main(){

    int k,i,j;
    cin>>n;
    for(int i=0;i<n;i++){
        father[i]=i;
        for(int j=0;j<n;j++){
            cin>>A[i][j];
        }
    }
    cout<<prim()<<endl;
    return 0;
}

C++: #include<iostream>

using namespace std;
#define MAX 100
#define INF 10000
int M[MAX][MAX];
int n;
int d[MAX];
int color[MAX];
int p[MAX];



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

  for (int i = 0; i < n; i++) {
    d[i] = INF;
    color[i] = 0;
  }

  int w = 0;
  d[0] = 0;
  while(true) {

    int com = INF;
    int u;
    for (int i = 0; i < n; i++) {
      if (color[i] != 2 && com > d[i] && d[i] != -1){
        com = d[i];
        u = i;
      }
    }

    if (com == INF) {
      break;
    }

    w += com;
    color[u] = 2;

    for (int j = 0; j < n; j++) {
      if (M[u][j] != -1 && M[u][j] < d[j] && color[j] != 2) {
        d[j] = M[u][j];
        p[j] = u;
      }
    }
  }

  cout << w << endl;
  return 0;
}

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

using namespace std;

const int NIL = 2001;
const int MAX = 100;
int G[MAX][MAX];
int color[MAX];
int W[MAX];
int n;

const int WHITE = 0;
const int GRAY = 1;
const int BLACK = 2;

void MST() {
	priority_queue<pair<int, int>> PQ;
	PQ.push(make_pair(0, 0));
	W[0] = 0;
	color[0] = BLACK;
	while (!PQ.empty()) {
		int u = PQ.top().second;
		PQ.pop();
		color[u] = BLACK;
		for (int i = 0; i < n; ++i) {
			if (G[u][i] != -1 && G[u][i] < W[i] && color[i] != BLACK) {
				PQ.push(make_pair(G[u][i] * -1, i));
				W[i] = G[u][i];
//				cout << u << ":" << i << ":" << G[u][i] << endl;
			}
		}
	}
}

int main() {

	scanf("%d", &n);
	for (int i = 0; i < n; ++i) {
		W[i] = NIL;
		color[i] = WHITE;
	}

	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			int a;
			scanf("%d", &a);
			G[i][j] = a;
		}
	}

	MST();

	cout << endl;

	int sum = 0;
	for (int i = 0; i < n; ++i) {
//		cout << i << ":" << W[i] << endl;
		sum += W[i];
	}
	cout << sum << endl;

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define WHITE 0
#define GRAY 1
#define BLACK 2

int M[101][101];
int n;
vector<int> q;

int check(int point){
    if(find(q.begin(), q.end(), point) != q.end()){
        //printf("%d in q\n",point);
        return 1;
    }
    else{
        //printf("%d not in q\n",point);
        return 0;
    }
}

int prim(int point){
    q.push_back(point);
    int dis = INT_MAX;
    int next_point;
    int sum = 0;
    while(q.size()!=n){
        dis = INT_MAX;
        for(int i=0;i<q.size();++i){
            for(int j=0;j<n;++j){
                if(M[q[i]][j] != INT_MAX && M[q[i]][j] < dis && check(j)==0){
                    dis = M[q[i]][j];
                    next_point = j;
                }
            }
        }
        q.push_back(next_point);
        //printf("push %d\n",next_point);
        sum += dis;
    }
    return sum;
}

int main(){
    int u, z, y;
    int value;
    scanf("%d",&n);
    for(int i=0;i<n;++i){
        for(int j=0;j<n;++j){
            cin>>value;
            M[i][j] = (value==-1)?INT_MAX:value;
            M[j][i] = (value==-1)?INT_MAX:value;
        }
    }
    int sum = prim(0);

    printf("%d\n",sum);
    return 0;
}