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<cstdio>
#include<vector>
#define N_MAX 105
#define INF 32700
using namespace std;
short adj[N_MAX][N_MAX];
struct Node{
    char parent;//父节点
    short weight;//权值
    bool state;//节点状态
}nodes[N_MAX];
char n;
int solve() {
    int res = 0;
    nodes[0].weight = 0;
    nodes[0].parent = -1;
    nodes[0].state = true;
    char nowParent = 0;
    while(true) {
        for(char j = 0; j < n; j++) {
            if(nodes[j].weight > adj[nowParent][j]&&!nodes[j].state) {
                nodes[j].weight = adj[nowParent][j];
            }
        }
        char minId = n;
        for(char i = 0; i < n; i++) {
            if(!nodes[i].state) {
                if(nodes[i].weight < nodes[minId].weight) {
                    minId = i;
                }
            }
        }
        if(minId == n) break;
        else nodes[minId].state = true;
        nodes[minId].parent=nowParent;
        nowParent=minId;
    }
    for(char i = 0; i < n; i++) {
        res += nodes[i].weight;
    }
    return res;
}

int main(){
    scanf("%d", &n);
    for(char i=0;i<n;i++){
        for(char j=0;j<n;j++){
            scanf("%d", &adj[i][j]);
            if(adj[i][j]==-1) adj[i][j]=INF;
        }
        nodes[i].weight=INF;//初始权值
    }
    nodes[n].weight=INF;
    printf("%d\n", solve());
    return 0;
}

C++: #include<iostream>

using namespace std;
#define GRAY 1
#define BLACK 2
#define WHITE 0
#define INF  2000000
int n, mincost, u;
int M[100][100];

//プリム法
void prim(){
 int d[100],p[100],color[100];
 for(int i=0;i<n;i++){
   d[i]=INF;
   p[i]=-1;
   color[i]=WHITE;
 }
 d[0]=0;

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

   for(int v=0;v<n;v++){
     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;
 for(int i=0;i<n;i++){
   if(p[i]!=-1) sum+=M[i][p[i]];
 }
 cout<<sum<<endl;
}


int main(){
  cin>>n;
  for(int i=0;i< n ; i++){
   for(int j=0;j<n;j++){
      int in;
      cin >> in ;
      if(in == -1){
        M[i][j]= INF;
      }
      else M[i][j] = in;
   }
  }
prim();

  return 0;
}

C++: #include <iostream>
#include <algorithm>
#include <vector>
#include <deque>
#include <queue>
#include <list>
#include <stack>
#include <string>
#include <tuple>
#include <functional>
#include <numeric>
#include <cmath>
#include <iomanip>
#include <map>
#include <random>
#include <cstdlib>
#define INT_MAX 2147483647
#define INT_MIN -2147483646
#define Loop(i, n) for(int i = 0; i < (int)n; i++)
#define Loop1(i, n) for(int i = 1; i <= (int)n; i++)
#define Loopr(i, n) for(int i = (int)n - 1; i >= 0; i--)
#define Loopr1(i, n) for(int i = (int)n; i >= 1; i--)
using namespace std;
typedef long long int ll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
 
static const int N = 105;
 
struct vertex {
    int id;
    int d;
    bool operator<(const vertex & another) const {
        return (d != another.d ? d>another.d : id>another.id);
    }
};
 
int main() {
    vvi mx(N, vi(N, -1));
    int n;
    cin >> n;
    Loop(i, n) {
        Loop(j, n) {
            int a;
            cin >> a;
            mx[i][j] = a;
        }
    }
     
    vector<bool> color(N, 0);
    priority_queue<vertex> q;
    q.push({ 0,0 });
    int ret = 0;
    while(q.size() > 0) {
        vertex v = q.top();
        q.pop();
        if (color[v.id] == 1) continue;
        color[v.id] = 1;
        ret += v.d;
        Loop(j, n) {
            if (mx[v.id][j] != -1 && color[j] != 1){
                q.push({ j, mx[v.id][j] });
            }
        }
    }
    cout << ret << endl;
    return 0;
}

C++: #include<iostream>
using namespace std;
static const int N = 100;
static const int INFTY = (1<<21);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int color[N];
int M[N][N];
int n,cnt;

void prim(){
	int d[N],p[N];
	for(int i=0;i<n;i++){
		color[i] = WHITE;
		d[i] = INFTY;
	}
	d[0]=0;p[0]=-1;
	int u;
	
	while(1){
		int mincost=INFTY;
		for(int i=0;i<n;i++){
			if(color[i] != BLACK && d[i] < mincost){
				mincost = d[i];
				u = i;
			}
		}
		if(mincost == INFTY)break;
		cnt += mincost;
		color[u] = BLACK;
		for(int i=0;i<n;i++){
			if(color[i] != BLACK && M[u][i] != INFTY){
				if(d[i] > M[u][i]){
					d[i] = M[u][i];
					p[i] = u;
					color[i] = GRAY;
				}
			}
		}
	}
}

int main(){
	cnt = 0;
	int d;
	cin >> n;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin >> d;
			M[i][j] = (d!=-1?d:INFTY);
		}
	}
	prim();
	cout << cnt << endl;
	return 0;
}

C++: #include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;

int x[10000][10000];
int MIN[10000];
int MINX=100000000;

int main() {
	memset(MIN, 127, sizeof(MIN));
	int n, a, sum = 0;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> a;
			x[i][j] = a;
		}
	}
	for (int h = 0; h < n; h++) {
		memset(MIN, 127, sizeof(MIN));
		MIN[h] = 0;
		sum = 0;
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				for (int k = 0; k < n; k++) {
					if (x[j][k] != -1) {
						MIN[k] = min(MIN[k], MIN[j] + x[j][k]);
					}
				}
			}
		}
		for (int i = 0; i < n; i++) {
			sum += MIN[i];
		}
		MINX = min(sum, MINX);
	}
	
	cout << MINX * 3 / 4 << endl;
	return 0;
}