Go: package main

import (
	"bufio"
	"container/heap"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	id     int
	weight int
}

func init() {
	sc.Split(bufio.ScanWords)
}

type NodeHeap []Node

func (h NodeHeap) Len() int           { return len(h) }
func (h NodeHeap) Less(i, j int) bool { return h[i].weight < h[j].weight }
func (h NodeHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }

func (h *NodeHeap) Push(x interface{}) {
	*h = append(*h, x.(Node))
}

func (h *NodeHeap) Pop() interface{} {
	old := *h
	n := len(old)
	x := old[n-1]
	*h = old[0 : n-1]
	return x
}

var sc = bufio.NewScanner(os.Stdin)

func scanInt() int {
	num, _ := strconv.Atoi(scanString())
	return num
}

func scanString() string {
	sc.Scan()
	return sc.Text()
}

func init() {
	sc.Split(bufio.ScanWords)
}

func main() {
	n := scanInt()

	list := make([][]int, n)
	seen := make([]bool, n)
	for i := range list {
		list[i] = make([]int, n)
		for j := range list[i] {
			list[i][j] = scanInt()
		}
	}

	start := Node{id: 0, weight: 0}
	h := &NodeHeap{start}
	heap.Init(h)

	sum := 0
	for h.Len() > 0 {
		node := heap.Pop(h).(Node)
		if seen[node.id] {
			continue
		}
		seen[node.id] = true
		sum += node.weight

		for i, w := range list[node.id] {
			if w < 0 {
				continue
			}
			heap.Push(h, Node{id: i, weight: w})
		}
	}

	fmt.Println(sum)
}

C++: #include<iostream>

using namespace std;

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 <set>
#include <map>
#include <list>
#include <queue>
#include <stack>
#include <cmath>
#include <ctime>
#include <cstdio>
#include <vector>
#include <string>
#include <bitset>
#include <cctype>
#include <cstdlib>
#include <cstring>
#include <utility>
#include <numeric>
#include <complex>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <cassert>
#include <iostream>
#include <iterator>
#include <algorithm>
using namespace std;
using ll = long long;
using VL=vector<ll>;

#define REP(i, n) for(int i = 0;i < n;i++)
#define REPR(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
const long long INF =  999999999;

typedef pair<int,int> P;

int cost[2010][2010];
int mincost[2020];
bool used[2020];
int V;

int main(){
  int n,res=0;
  cin>>n;
  REP(i,n){
    REP(j,n){
      cin>>cost[i][j];
    }
  }
  REP(i,n){
    mincost[i]=INF;
    used[i]=false;
  }
  mincost[0]=0;

  while(true){
    int v=-1;

    REP(u,n){
      if(!used[u] &&(v==-1 || mincost[u]<mincost[v]))v=u;
    }

    if(v==-1)break;
    used[v]=true;
    res += mincost[v];

    REP(u,n){
      if(cost[v][u]==-1)continue;
      mincost[u]=min(mincost[u],cost[v][u]);
    }
  }
  cout<<res<<endl;

}

C++: #include <bits/stdc++.h>

#define REP(i, n) for(int i = 0; i < n; i++)
using namespace std;

int P[10010];

void init(int N)
{
    for (int i = 0; i < N; i++) P[i] = i;
}

int root(int a)
{
    if (P[a] == a)  return a;
    return (P[a] = root(P[a]));
}

bool is_same_set(int a, int b)
{
    return root(a) == root(b);
}

void unite(int a, int b)
{
    P[root(a)] = root(b);
}

int main()
{   
    int n;
    cin >> n;

    vector<tuple<int, int, int>> pr;
    int a;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> a;
            if (a != -1 && i <= j) {
                pr.push_back(make_tuple(a, i, j));
            }
        }
    }

    sort(pr.begin(), pr.end());
    init(n);
    int cost = 0;

    for (int i = 0; i < pr.size(); i++) {
        int& a = get<1>(pr[i]);
        int& b = get<2>(pr[i]);

        if (!is_same_set(a, b)) {
            unite(a, b);
            cost += get<0>(pr[i]);
        }
    }
    cout << cost << endl;
}

C++: #include <iostream>

using namespace std;
static const int MAX = 100;
static const int INF = (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] = INF;
        p[i] = -1;
        color[i] = WHITE;
    }

    d[0] = 0;

    while (true) {
        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 <iostream>
#include <cstdio>
#include <cstring>
#define MAX 105
#define INF 1000000
using namespace std;

int n;
int M[MAX][MAX];
int d[MAX];
int p[MAX];
int color[MAX];//0 表示未进入 -1 表示在之中 1 表示已出去

int prim() {
	int u,min,i,j;
	d[0]=0;
	p[0]=-1;
	while(1) {
		min=INF;
		u=-1;
		for(i=0; i<n; i++) {
			if(min>d[i] && color[i]!=1) {
				u=i;
				min=d[i];
			}
		}
		if(u==-1) break;
		color[u]=1;
		for(j=0; j<n; j++) {
			if(color[j]!=1 && M[u][j]!=INF) {
				if(d[j]>M[u][j]) {
					d[j]=M[u][j];
					color[j]=-1;
					p[j]=u;
				}
			}
		}
	}
	int sum=0;
	for(i=0; i<n; i++) {
		if(p[i] != -1) sum+=M[i][p[i]];
	}
	return sum;
}

int main() {
	int i,j,a;
	memset(color,0,sizeof(color));
	memset(d,INF,sizeof(d));
	memset(p,-1,sizeof(p));
	scanf("%d",&n);
	for(i=0; i<n; i++) {
		for(j=0; j<n; j++) {
			scanf("%d",&a);
			if(a==-1) a=INF;
			M[i][j]=a;
		}
	}
	cout<<prim();
	return 0;
}