Go: package main

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

var scanner = bufio.NewScanner(os.Stdin)

func nextString() string {
	scanner.Scan()
	return scanner.Text()
}

func nextInt() int {
	n, err := strconv.Atoi(nextString())
	if err != nil {
		fmt.Printf("strconv.Atoi failed: %v\n", err)
	}
	return n
}

type ElementKey int
type Node struct {
	key    ElementKey
	parent *Node
	rank   int
}

func newNode(key ElementKey) *Node {
	node := Node{}
	node.key = key
	node.parent = &node
	node.rank = 0

	return &node
}

func union(x, y *Node) {
	xSet := findSet(x)
	ySet := findSet(y)
	link(xSet, ySet)
}

func link(x, y *Node) {
	if x.rank > y.rank {
		y.parent = x
	} else {
		x.parent = y

		if x.rank == y.rank {
			y.rank++
		}
	}
}

func findSet(x *Node) *Node {
	if x != x.parent {
		x.parent = findSet(x.parent)
	}
	return x.parent
}

func newDisjointSets(nSets int) *DisjointSets {
	sets := DisjointSets{}
	sets.keyToNode = map[ElementKey]*Node{}
	for i := 0; i < nSets; i++ {
		key := ElementKey(i)
		sets.keyToNode[key] = newNode(key)
	}
	return &sets
}

type DisjointSets struct {
	keyToNode map[ElementKey]*Node
}

func (sets *DisjointSets) union(x, y ElementKey) {
	xNode := sets.keyToNode[x]
	yNode := sets.keyToNode[y]
	union(xNode, yNode)
}

func (sets DisjointSets) findSet(x ElementKey) *Node {
	xNode := sets.keyToNode[x]
	return findSet(xNode)
}

type Edge struct {
	i, j   int
	weight int
}

func main() {
	scanner.Split(bufio.ScanWords)

	n := nextInt()
	sets := newDisjointSets(n)
	edges := []Edge{}
	a := make([][]int, n)
	for i := 0; i < n; i++ {
		a[i] = make([]int, n)
		for j := 0; j < n; j++ {
			a[i][j] = nextInt()
			if a[i][j] >= 0 {
				e := Edge{
					i:      i,
					j:      j,
					weight: a[i][j],
				}
				edges = append(edges, e)
			}
		}
	}
	sort.Slice(edges, func(i, j int) bool { return edges[i].weight < edges[j].weight })
	totalWeight := 0
	for _, edge := range edges {
		i := ElementKey(edge.i)
		j := ElementKey(edge.j)
		if sets.findSet(i) != sets.findSet(j) {
			totalWeight += edge.weight
			sets.union(i, j)
		}
	}
	fmt.Println(totalWeight)
}

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;
}