Go: package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

C++: #include<bits/stdc++.h>
using namespace std;
const int MAX=100;
const int INF=(1<<21);
const int WHI=0;
const int GRA=1;
const int BLA=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]=INF;
    p[i]=-1;
    color[i]=WHI;
  }

  d[0]=0;
  while(1){
    minv=INF;
    u=-1;

    for(int i=0;i<n;i++){
      if(minv>d[i] && color[i]!=BLA){
	u=i;
	minv=d[i];
      }
    }

    if(u==-1){
      break;
    }

    color[u]=BLA;//ここで訪問に記録

    for(int v=0;v<n;v++){
      if(color[v]!=BLA && M[u][v]!=INF){//まだ行くところがある && u,vに辺が通っている
	if(M[u][v]<d[v]){
	  d[v]=M[u][v];
	  p[v]=u;
	  color[v]=GRA;
	}
      }
    }
  }
  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;
      if(e==-1){
	M[i][j]=INF;
      }else{
	M[i][j]=e;
      }
    }
  }
  cout<<prim()<<endl;

  return 0;
}

C++: #include<iostream>
using namespace std;
#define MAX 100
#define INF (1<<21)
#define WHITE 0
#define GRAY 1
#define 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] = INF;
    p[i] = -1;
    color[i] = WHITE;
  }

  d[0] = 0;

  while(1){
    minv = INF;
    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] != 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]];
  }
  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) ? INF : e;
    }
  }
  cout << prim() << endl;
  
  return 0;
}

C++: #include<cstdio>
#include<queue>
using namespace std;

static const int MAX = 100;
static const int INFTY = (1 << 30);
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;

int color[MAX];
int M[MAX][MAX];
int d[MAX];
int p[MAX];
int n;
int prim()
{
	int u, minv;
	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()
{
	scanf("%d", &n);

	for(int i=0; i<n; i++)
	{
		for(int j=0; j<n; j++)
		{
			int e;
			scanf("%d", &e);
			M[i][j] = (e == -1) ? INFTY:e;
		}
	}

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

	return 0;
}

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

typedef long long ll;

#define MAX_V 100
#define INF int(1e9)

// g : ??°??????, V : g???????????°, s : ????????????????????????
int Prim (int g[MAX_V + 1][MAX_V + 1], int V, int s) {
    ll ret = 0, min_, nxtv, v = s, size_;
    // bool used[V] = {false}; // c++11??????
    bool used[V]; memset(used, 0, sizeof(used)); // c++11??\???
    vector<int> usedv;
    usedv.push_back(s);
    used[s] = true;

    while (usedv.size() < V) {
        min_ = INF;
        size_ = usedv.size();

        // ?????¨???????????????????????°?????????????????\?¶????????????????????°????????????¢???
        for (int i = 0; i < size_; ++i) {
            for (int j = 0; j < V; ++j) {
                if (usedv[i] == j) continue;
                if (!used[j] && min_ > g[usedv[i]][j]) {
                    min_ = g[usedv[i]][j];
                    v = j;
                }
            }
        }

        ret += min_;
        usedv.push_back(v);
        used[v] = true;
    }

    return ret;
}

int n, g[MAX_V + 1][MAX_V + 1];

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> n;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            cin >> g[i][j];
            if (g[i][j] == -1) g[i][j] = INF;
        }
    }

    cout << Prim(g, n, 0) << endl;


    return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
static const int MAX=100;
static const int INF=(1<<21);
static const int WHI=0;
static const int GRA=1;
static const int BLA=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]=INF;
    p[i]=-1;
    color[i]=WHI;
  }
  d[0]=0;
  while(1){
    minv=INF;
    u=-1;
    for(int i=0;i<n;i++){
      if(minv>d[i]&&color[i]!=BLA){
	u=i;
	minv=d[i];
      }
    }
    if(u==-1) break;
    color[u]=BLA; //ここで訪問に記録
    for(int v=0;v<n;v++){
      if(color[v]!=BLA&&M[u][v]!=INF){
	if(M[u][v]<d[v]){
	  d[v]=M[u][v];
	  p[v]=u;
	  color[v]=GRA;
	}
      }
    }
  }
  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;
      if(e==-1){
	M[i][j]=INF;
      }else{
	M[i][j]=e;
      }
    }
  }
  cout<<prim()<<endl;
  return(0);
}