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>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)   for(int i=0;i<(n);++i)
#define SORT(c)    sort((c).begin(),(c).end())
#define CLR(a)     memset((&a), 0 ,sizeof(a))//clear memory
#define dump(x)    cerr << #x << " = " << (x) << endl;//debug
#define debug(x)   cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#define EPS        1e-10//sample:if((double)>=(double)+EPS)
//cin,cout release
//std::cin.tie(0);
//ios::sync_with_stdio(false);
#define MAX 100
using namespace std;
int n,A[MAX][MAX];
bool r[101][101]={};
#define WHITE 0
#define GRAY 1
#define BLACK 2
int prim(){
  int u;
  int d[MAX],pi[MAX],color[MAX];
  int mincost;
  rep(i,n){
    d[i]=INT_MAX;
    pi[i]=-1;
    color[i]=0;
  }
  d[0]=0;

  while(1){
    mincost=INT_MAX;
    u=-1;
    rep(i,n)
      if(mincost>d[i]&&color[i]!=BLACK){
	u=i;
	mincost=d[i];
      }
    if(u==-1)break;
    color[u]=BLACK;
    rep(v,n){
      if(color[v]!=BLACK&&A[u][v]!=INT_MAX){
	if(d[v]>A[u][v]){
	  d[v]=A[u][v];
	  pi[v]=u;
	  color[v]=GRAY;
	}
      }
    }
  }
  int sum=0;
  rep(i,n)if(pi[i]!=-1)sum+=A[i][pi[i]];
  return sum;
}
int main(){
  int a;
  cin>>n;
  rep(i,n)rep(j,n){
    cin>>a;
    if(a==-1)A[i][j]=INT_MAX;
    else A[i][j]=a;
  }
  cout<<prim()<<endl;

  return 0;
}

C++: #include <iostream>
#include <sstream>
#include <iomanip>
#include <algorithm>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <climits>

#define LP(i,n) for(int i=0;i<n;i++)
#define Mset(x,v) memset(x,v,sizeof(x))

using namespace std;
using LL=long long;

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 INF=(1<<21);
static const int WH=0;
static const int GRY=1;
static const int BL=2;

int n, MA[MAX][MAX];

int prim(){
  int  u, minV;
  int d[MAX], p[MAX], color[MAX];

  for(int i=0; i<n; i++)
  {
    d[i]=INF;
    p[i] = -1;
    color[i]=WH;
  }

  d[0]=0;

  while(1)
  {
    minV=INF;
    u = -1;
    for(int i=0; i<n; i++)
    {
      if(minV > d[i] && color[i] != BL)
      {
        u=i;
        minV=d[i];
      }
    }
    if(u == -1) break;
    color[u]=BL;
    for(int v=0; v<n; v++)
    {
      if(color[v] != BL && MA[u][v] != INF)
      {
        if(d[v] > MA[u][v])
        {
          d[v]=MA[u][v];
          p[v]=u;
          color[v]=GRY;
        }
      }
    }
  }
  int sum=0;
  for(int i=0; i<n; i++)
  {
    if(p[i] != -1) sum += MA[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;
      MA[i][j] = (e == -1) ? INF : e;
    }
  }

  cout << prim() << endl;

  return 0;
}

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

#define WHITE 0
#define GRAY 1
#define BLACK 2
#define INF 114514

int x[10000][10000];
int color[10000];
int MIN[10000];
int sum;
int sum_min = INF;

int main() {
	int n, a, b, c;
	cin >> n;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			cin >> x[i][j];
		}
	}
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			MIN[j] = INF;
			color[j] = WHITE;
		}
		b = INF;
		a = n;
		color[i] = GRAY;
		MIN[i] = 0;
		while (a != 0) {
			b = INF;
			for (int j = 0; j < n; j++) {
				if (color[j] == GRAY) {
					if (b > MIN[j]) {
						b = MIN[j];
						c = j;
					}
				}
			}
			color[c] = BLACK;
			a -= 1;
			for (int k = 0; k < n; k++) {
				if (color[k] != BLACK && x[c][k] != -1) {
					color[k] = GRAY;
					MIN[k] = min(x[c][k], MIN[k]);
				}
			}
		}
		sum = 0;
		for (int j = 0; j < n; j++) {
			sum += MIN[j];
		}
		sum_min = min(sum_min, sum);
	}
	cout << sum_min << endl;
	return 0;
}

C++: #include <stdio.h>
#define INFTY 1000000
#define M -1
#define WHITE 0
#define GRAY  1
#define BLACK 2
#define N 100
int prim(void);
int n,A[N][N];

int main()
{
  int i,j,k;

  scanf("%d",&n);
  for(i=0;i<n;i++)
    {
      for(j=0;j<n;j++)
        {
          scanf("%d",&k);
          if(k==M) A[i][j]=INFTY;
        }
    }

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

int prim()
{
  int d[N],p[N],color[N];
  int i,v,u,mincost,sum=0;

  for(i=0;i<n;i++)
    {
      d[i]=INFTY;
      p[i]=M;
      color[i]=WHITE;
    }
  d[0]=0;
while(1)
    {
      mincost=INFTY;
      u=M;
      for(i=0;i<n;i++)
        {
          if(color[i]!=BLACK&&d[i]<mincost)
            {
              u=i;
              mincost=d[i];
            }
        }
      if(u==M) break;
      color[u]=BLACK;
      for(v=0;v<n;v++)
        {
          if(color[v]!=BLACK&&A[u][v]!=INFTY)
            {
              if(d[v]>A[u][v])
                {
                  d[v]=A[u][v];
                  p[v]=u;
                  color[v]=GRAY;
                }
            }
        }
    }
  for(i=0;i<n;i++)
    {
      if(p[i]!=M) sum+=A[i][p[i]];
    }
  return sum;