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>

const int MAX = 101;
const int NIL = -1; 
const int UPBOUND = (1 << 20);

using namespace std;

int prim(int adj_matrix[][MAX], int n, int u);


int main()
{
	int adj_matrix[MAX][MAX] = {0};		
	
	int n;
	cin >> n;

	for (int i = 1; i <= n; i++)
	{
		for (int j = 1; j <= n; j++)
		{
			int e; cin >> e;
			adj_matrix[i][j] = e == -1? UPBOUND: e;
		}
	}
	
//	for (int i = 0; i < n; i++)
//	{
//		for (int j = 0; j < n; j++)
//		{
//			cout << adj_matrix[i][j] << " ";
//		}
//		cout << endl;
//	}

	
	cout << prim(adj_matrix, n, 1) << endl;
} 


int prim(int adj_matrix[][MAX], int n, int u)
{
	int cost[MAX]; //记录最小权值
	int edge[MAX]; //记录选中的边
	
	
	for (int v = 1; v <= n; v++)
	{
		cost[v] = adj_matrix[u][v];
		edge[v] = u;
	}	 
	
	cost[u] = NIL; //排除u 
	
	while (true)
	{
		int w = NIL;
		int min = 3000; //权值上限 
		for (int v = 1; v <= n; v++)
		{
			if (cost[v] != NIL && cost[v] < min)
			{
				min = cost[v];
				w = v;
			} 
		}
		
		if (w == NIL) break;
		
		cost[w] = NIL;
		
		//更新最小权值数组 
		for (int v = 1; v <= n; v++)
		{
			if (cost[v] > adj_matrix[w][v] && adj_matrix[w][v] != NIL)
			{
				cost[v] = adj_matrix[w][v];
				edge[v] = w;			
			}
		}
				
	}
	
	
	//求生成树的权值
	int sum = 0;
	for (int v = 1; v <= n; v++)
	{
		if (v != u)
		sum += adj_matrix[v][edge[v]];
	} 
	
	return sum;	
	
}

C++: #include <iostream>
#include <limits>

constexpr int MAXN = 100;
int G[MAXN][MAXN];
int P[MAXN];
int D[MAXN];
int C[MAXN];

int main(){
    int n;
    std::cin >> n;
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < n; j++) {
            std::cin >> G[i][j];
            if (G[i][j] == -1) {
                G[i][j] = std::numeric_limits<int>::max();
            }
        }
    }

    for (int i = 0; i < n; i++) {
        D[i] = std::numeric_limits<int>::max();
    }

    D[0] = 0;
    P[0] = -1;
    while (true) {
        int m;
        int mincost = std::numeric_limits<int>::max();
        for (int i = 0; i < n; i++) {
            if ((C[i] == 0) && (D[i] < mincost)) {
                mincost = D[i];
                m = i;
            }
        }

        if (mincost == std::numeric_limits<int>::max()) {
            break;
        }

        C[m] = 1;
        D[m] = mincost;

        for (int i = 0; i < n; i++) {
            if ((G[m][i] < std::numeric_limits<int>::max()) && (C[i] == 0) && (G[m][i] < D[i])) {
                D[i] = G[m][i];
            }
        }
    }


    int sum = 0;
    for (int i = 0; i < n; i++) {
        if (D[i] != std::numeric_limits<int>::max()) {
            sum += D[i];
        }
    }
//    for (int i = 0; i < n; i++) {
//        std::cout << i << ": " << D[i] << std::endl;
//    }
    std::cout << sum << std::endl;

}

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 (true) {
		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++) {
			cin >> M[i][j];
			if (M[i][j] == -1)M[i][j] = INFTY;
		}
	}
	cout << prim() << '\n';
	return 0;
}

C++: #include<iostream>
#include<vector>
#include<queue>
using namespace std;
template< typename FirstType, typename SecondType >
struct PairComparator {
  bool operator()( const pair<FirstType, SecondType>& p1, const pair<FirstType, SecondType>& p2 ) const 
    {  
		return p1.first > p2.first;
    }
};
bool inMST(vector< std::pair<int,int> > & MST,int j) {
	for (int k=0;k<(int)MST.size();++k){
		if(j == MST[k].second)
			return true;
	}
	return false;
}
int main(){
	int n;
	cin >> n;
	vector<int> E(n*n);
	vector< std::pair<int,int> > MST;

	for(int k=0;k<n*n;++k) {
		cin >> E[k];
	}
	priority_queue<pair<int,pair<int,int> >,vector< pair<int,pair<int,int> > >,
		PairComparator<int,pair<int,int> > > r;

	//put Node 0
	int cost = 0;
	int i=0;
	MST.push_back(pair<int,int>(i,i));
	while((int)MST.size() < n) {
		int ii=i*n;
		for (int j=0;j<n;++j) {
			if (E[ii+j] >= 0) {
				pair<int,int> add = std::make_pair(i,j);
				if (!inMST(MST,add.second)){
					r.push(std::pair<int,std::pair<int,int> >(E[ii+j],add));
				}
			}
		}
		pair<int,pair<int,int> > top;
		while (!r.empty()) {
			top = r.top();
			r.pop();
			if (!inMST(MST,top.second.second)){
				break;
			}
		}
		cost += top.first;
		MST.push_back(top.second);
		i = top.second.second;
	}
	cout << cost << endl;
}