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<bits/stdc++.h>

std::vector<int> color;
std::vector<std::vector<int>> M;
std::vector<int> d;
std::vector<int> p;
int INF = 1001001001;
int sum = 0;

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

    d[0] = 0;
    p[0] = -1;

    while(true){
        int u;
        int mincost = INF;
        for(int i = 0; i < n; i++){
            if(color[i] != 1 && d[i] < mincost){
                mincost = d[i];
                u = i;
            }
        }

        if(mincost == INF){
            break;
        }

        color[u] = 1;

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

    }
    
    for(int i = 0; i < d.size(); i++){
        sum += d[i];
    }

    return sum;
}

int main(void){
    int n;
    std::cin >> n;

    color.resize(n);
    M.resize(n, std::vector<int>(n));
    d.resize(n);
    p.resize(n);

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

    std::cout << prim(n) << std::endl;

    return 0;
}

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

int n;
int a[101][101];

set<int>s,t;

int main(){
	s = set<int>();
	t = set<int>();
	scanf("%d",&n);
	for(int i = 0; i < n; i++){
		for(int j = 0; j < n; j++){
			scanf("%d",&a[i][j]);
		}
		if(i == 0){
			t.insert(i);
		}
		else{
			s.insert(i);
		}
	}
	int ans = 0;
	while(!s.empty()){
		int min_s=-1,min_t=-1,min_w=10000000;
		for(set<int>::iterator sit = s.begin(); sit != s.end(); sit++){
			for(set<int>::iterator tit = t.begin(); tit != t.end(); tit++){
				if(a[*sit][*tit] != -1 && a[*sit][*tit] < min_w){
					min_s = *sit;
					min_t = *tit;
					min_w = a[*sit][*tit];
				}
			}
		}
		s.erase(min_s);
		t.insert(min_s);
		ans += min_w;
	}
	printf("%d\n",ans);
	
	return 0;
}

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

static const int MAX = 100;
static const int INF = (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];

    rep(i,n) {
        d[i] = INF;
        p[i] = -1;
        color[i] = WHITE;
    }
    d[0] = 0;

    while(1){
        minv = INF;
        u = -1;
        rep(i,n) {
            if( minv > d[i] && color[i] != BLACK) {
                u = i;
                minv = d[i];
            }
        }
        if (u == -1) break;
        color[u] = BLACK;
        rep(v,n) {
            if (color[v] != BLACK && M[u][v] != INF) {
                if ( d[v] > M[u][v]){
                    d[v] = M[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }
    int sum = 0;
    rep(i,n) {
        if (p[i] != -1) sum += M[i][p[i]];
    }
    return sum;
}

int main(){
    cin >> n;
    rep(i,n){
        rep(j,n){
            int e; cin >> e;
            M[i][j] = (e == -1)? INF : e;
        }
    } 
    cout << prim() << endl;
    return 0;
}

C++: #include <stdio.h>
#define MAX 1 << 22
int map[1000][1000];
int n, minval = 999999;

int prim()
{
    int sum = 0;
    int d[1000], fathernode[1000], color[1000];;
    for(int i = 0; i < n; i ++)
        d[i] = fathernode[i] = MAX;
    d[0] = 0;
    while(true)
    {
        int ch = -1, min = MAX;
        for(int i = 0; i < n; i ++)
        {
            if(min > d[i] && color[i] == 0) //选取未被染色的点
            {
                ch = i;
                min = d[i];
            }
        }
        if(ch == -1) //选完了，跳出
            break;
        color[ch] = 1;//选取这个点后染色
        for(int j = 0; j < n; j ++)//选取V-T中与T距离最近的节点
        {
            if(d[j] > map[ch][j] && color[j] == 0)
            {
                d[j] = map[ch][j];
                fathernode[j] = ch;//j节点的父节点是ch
            }
        }
    }
    //选取完毕，开始加起来
    for(int k = 0; k < n; k ++)//只加被染色（即被选中的）节点
    {
        if(fathernode[k] != MAX)//只加上有父节点的点
            sum += map[k][fathernode[k]];
    }
    return sum;
}

int main(void)
{
    scanf("%d", &n);
    for(int i = 0; i < n; i ++)
        for(int j = 0; j < n; j ++)
        {
            int t;
            scanf("%d", &t);
            map[i][j] = (t == -1 ? MAX : t);
        }
    printf("%d\n", prim() );
    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 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 = 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<cstdio>
#include<queue>
#include<map>
using namespace std;
typedef pair< int, int > Pi;
int info[100][100];
bool used[100];

int prim(const int& V){
  priority_queue< Pi > que;
  que.push(Pi());
  int ret = 0;
  while(!que.empty()){
    Pi p = que.top(); que.pop();
    if(!~-p.first || used[p.second]++) continue;
    ret -= p.first;
    for(int i = 0; i < V; i++) que.push( Pi( -info[p.second][i], i));
  }
  return ret;
}

int main(){
  int N;
  scanf("%d", &N);
  for(int i = 0; i < N; i++){
    for(int j = 0 ; j < N ; j++){
      scanf("%d", &info[i][j]);
    }
  }
  printf("%d\n", prim(N));
}