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<vector>
#include<algorithm>
#include<queue>
#include<cstring>
#define P pair<int , int>
using namespace std;

int main(){
  int n, a[109][109];
  bool check[109];
  priority_queue<P, vector<P>, greater<P> > Q;
  cin >> n;
  for(int i=0;i<n;i++){
    for(int j=0;j<n;j++)cin >> a[i][j];
  }
  memset(check, false, sizeof(check));
  int ans = 0;
  Q.push(P(0, 0));
  while(!Q.empty()){
    P p = Q.top();Q.pop();
    if(check[p.second])continue;
    ans += p.first;
    check[p.second] = true;
    for(int i=0;i<n;i++){
      if(!check[i] && a[p.second][i]!=-1){
        Q.push(P(a[p.second][i], i));
      }
    }
  }
  cout << ans << endl;
}

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 (1) {
    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 (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;

  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 a, min;
   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 ( 1 ) {
      min = INFTY;
      a = -1;
   
      for ( int i = 0; i < n; i++ ) {
         if ( min > d[i] && color[i] != BLACK ) {
            a = i;
            min = d[i];
         }
      }
   
      if ( a == -1 ) break;
      color[a] = BLACK;
      for ( int v = 0; v < n; v++ ) {
         if ( color[v] != BLACK && M[a][v] != INFTY ) {
            if ( d[v] > M[a][v] ) {
               d[v] = M[a][v];
               p[v] = a;
               color[v] = GRAY;
            }
         }
      }
   }
   
   int sum = 0;
   for ( int i = 0; i < n; i++ ) {
      if ( p[i] != -1 ) sum = 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 <vector>
#include <queue>
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[u][v]?????°???u??°v???????????????
int M[MAX][MAX];

struct segment{
    //??????
    int start;
    //??????
    int end;
    //??????
    int dis;

    segment(int s,int e,int d):start(s),end(e),dis(d){}

    bool operator < (const segment& p)const {
        return dis<p.dis;
    }
};

int prim(){
    //????????¶???
    int u=0;
    //??¨?????°???MST?????¶???V?????¶??????
    int p[MAX];
    //??¨?????°???v???????????¶???WHITE???GRAY???BLACK
    int color[MAX];
    //??¨?????°????????\T?????¶??????V-T?????¶?????????????????????????°????????????????
    priority_queue<segment,vector<segment> > d;

    //init
    for(int i=0;i<n;i++){
        p[i]=-1;
        color[i]=WHITE;
    }

    while(true){
        bool ok=true;
        for(int i=0;i<n;i++)
            if(color[i]==WHITE){
                ok= false;
                break;
            }
        if(ok)
            break;

        color[u]=BLACK;
        for(int i=0;i<n;i++)
            if(i!=u&&color[i]==WHITE&&M[u][i]!=INFTY){
                color[i]=GRAY;
                d.push(segment(u,i,M[u][i]));
            }
        u=d.top().end;
        p[u]=d.top().start;
        d.pop();
    }

    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++: #include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i=0; i<(n); i++)

#define NIL -1
#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INF 1 << 21

int prim(vector<vector<int> > &graph, int n){

    vector<int> parent(n, NIL);
    vector<int> cost(n, INF);
    vector<int> color(n, WHITE);

    cost[0] = 0;
    while(1){
        int minv = INF;
        int u = NIL;
        rep(i, n){
            if(cost[i] < minv && color[i] != BLACK){
                minv = cost[i];
                u = i;
            }
        }
        if(u == NIL) break;

        color[u] = BLACK;
        rep(j, n){
            if(color[j] != BLACK && graph[u][j] != NIL){
                if(cost[j] > graph[u][j]){
                    cost[j] = graph[u][j];
                    parent[j] = u;
                    color[j] = GRAY;
                }
            }
        }
    }

    int sum = 0;
    rep(i, n){
        if(parent[i] != NIL){
            sum += graph[i][parent[i]];
        }
    }
    return sum;
}

int main() {

    int n;
    cin >> n;
    vector<vector<int> > graph(n, vector<int>(n));
    rep(i, n){
        rep(j, n){
            cin >> graph[i][j];
        }
    }

    cout << prim(graph, n) << endl;

    return 0;
}