Go: package main

import (
	"fmt"
	"sort"
)

type Edge struct {
	I int
	J int
	A int
}

func main() {
	var n int
	fmt.Scan(&n)

	g := make([][]int, n)
	edges := make([]Edge, 0, n*(n-1)/2)
	parents := make([]int, n)
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		for j := 0; j < n; j++ {
			fmt.Scan(&g[i][j])
			if g[i][j] > 0 {
				edges = append(edges, Edge{i, j, g[i][j]})
			}
		}
		parents[i] = i
	}
	sort.SliceStable(edges, func(i, j int) bool { return edges[i].A > edges[j].A })

	sum := 0
	for len(edges) > 0 {
		edge := edges[len(edges)-1]
		edges = edges[:len(edges)-1]

		if same(edge.I, edge.J, &parents) {
			continue
		}
		union(edge.I, edge.J, &parents)
		sum += edge.A
	}
	fmt.Println(sum)
}



func root(id int, parents *[]int) int {
	if id == (*parents)[id] {
		return id
	}
	return root((*parents)[id], parents)
}

func union(i, j int, parents *[]int) {
	(*parents)[root(j, parents)] = (*parents)[root(i, parents)]
}

func same(i, j int, parents *[]int) bool {
	return root(i, parents) == root(j, parents)
}

C++: #include<iostream>
using namespace std;
#define INFTY (1 << 30)

enum Color {
	WHITE,
	GRAY,
	BLACK,
};

void Prim(int verValWeight[][100], int verNum) {
	int distance[100];
	Color color[100];
	int parent[100];
	for (int i = 0; i < verNum; i++) {
		color[i] = WHITE;
		distance[i] = INFTY;
		parent[i] = -1;
	}
	distance[0] = 0;

	while (true) {
		int min_cost = INFTY;
		int subScript;
		for (int i = 0; i < verNum; i++) {
			if (color[i] != BLACK && distance[i] < min_cost) {
				min_cost = distance[i];
				subScript = i;
			}
		}

		if (min_cost == INFTY)
			break; //end

		color[subScript] = BLACK;

		for (int i = 0; i < verNum; i++) {
			if (color[i] != BLACK && verValWeight[subScript][i] != INFTY) {
				if (verValWeight[subScript][i] < distance[i]) {
					distance[i] = verValWeight[subScript][i];
					parent[i] = subScript;
					color[i] = GRAY;
				}
			}
		}
	}

	int weight_sum = 0;
	for (int i = 0; i < verNum; i++)
		weight_sum += distance[i];
		//if (parent[i] != -1)
		//	weight_sum += verValWeight[i][parent[i]];
	cout << weight_sum << endl;

}

int main() {
	int verNum;
	int verValWeight[100][100];
	int parent[100];

	cin >> verNum;
	for (int i = 0; i < verNum; i++)
		for (int j = 0; j < verNum; j++) {
			cin >> verValWeight[i][j];
			if (verValWeight[i][j] == -1) verValWeight[i][j] = INFTY;
		}

	Prim(verValWeight, verNum);

	return 0;
}

C++: #include<cstdio>
#include<algorithm>
#include<queue>
#include<map>
using namespace std;
typedef pair< int, int > Pi;
const int INF = 1 << 30;
int info[100][100];
bool used[100];

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

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;
}