Go: package main

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

const (
	white int = iota
	gray
	black
)
const INFTY int = 2001

var G [][]int
var color []int
var d []int
var p []int
var N int

func prim() int {
	u := 0
	d[u] = 0
	for {
		minCost := INFTY
		for i:=0; i<N; i++ {
			if color[i] != black && d[i] < minCost {
				minCost = d[i]
				u = i
			}
		}

		if minCost == INFTY {
			break
		}

		color[u] = black

		for v:=0; v<N; v++ {
			if color[v] != black && G[u][v] != -1 {
				if G[u][v] < d[v] {
					d[v] = G[u][v]
					p[v] = u
					color[v] = gray
				}
			}
		}
	}
	// sum
	sum := 0
	for i:=0; i<N; i++ {
		if p[i] != -1 {
			sum += G[i][p[i]]
		}
	}
	return sum
}




func initVariable(N int) {
	G = make([][]int, N)
	for i:=0; i<N; i++ {
		G[i] = make([]int, N)
	}
	color = make([]int, N)
	d = make([]int, N)
	p = make([]int, N)
	for i:=0; i<N; i++ {
		d[i] = INFTY
		p[i] = -1
	}
}

func nextInt(scanner *bufio.Scanner) int {
	scanner.Scan()
	num, _ := strconv.Atoi(scanner.Text())
	return num
}

func main() {
	scanner := bufio.NewScanner(os.Stdin)
	scanner.Split(bufio.ScanWords)
	N = nextInt(scanner)
	initVariable(N)
	for i:=0; i<N; i++ {
		for j:=0; j<N; j++ {
			G[i][j] = nextInt(scanner)
		}
	}
	fmt.Printf("%d\n", prim())
}

C++: #include <algorithm>
#include <iostream>
#include <vector>

class TEdge;
struct TNode
{
	int TreeIndex;
	std::vector<const TEdge*> Connected;
	
	TNode();
	void SetIndex(int Index, const TEdge* Edge);
};

class TEdge
{
	std::pair<TNode*, TNode*> FEnds;
	int FWeight;
public:
	TEdge(TNode* EndA, TNode* EndB, int Weight);
	
	bool operator<(const TEdge& Other)const;
	int  Weight()const {return FWeight;}
	bool ToMekeCycle()const;
	
	void JoinTree(int TreeIndex)const;
};

TNode::TNode()
:TreeIndex(0)
{
}

void TNode::SetIndex(int Index, const TEdge* Edge)
{
	if(TreeIndex >= Index) return;
	TreeIndex = Index;
	for(std::vector<const TEdge*>::const_iterator It = Connected.begin(); It != Connected.end(); ++It){
		(*It)->JoinTree(Index);
	}
	Connected.push_back(Edge);
}

TEdge::TEdge(TNode* EndA, TNode* EndB, int Weight)
:FEnds(EndA, EndB), FWeight(Weight)
{
}

bool TEdge::operator<(const TEdge& Other)const
{
	return Weight() < Other.Weight();
}

bool TEdge::ToMekeCycle()const
{
	return FEnds.first->TreeIndex > 0 && FEnds.first->TreeIndex == FEnds.second->TreeIndex;
}

void TEdge::JoinTree(int TreeIndex)const
{
	FEnds.first->SetIndex(TreeIndex, this);
	FEnds.second->SetIndex(TreeIndex, this);
}

class TGraph
{
	std::vector<TNode> FNodes;
	std::vector<TEdge> FEdges;
public:
	TGraph(int NodeCount);
	
	void AddEdge(int NodeIndexA, int NodeIndexB, int Weight);
	int WeightMinimumSpanningTree();
};

TGraph::TGraph(int NodeCount)
:FNodes(NodeCount)
{
}

void TGraph::AddEdge(int NodeIndexA, int NodeIndexB, int Weight)
{
	if(NodeIndexA <= NodeIndexB || Weight < 0) return;
	FEdges.push_back(TEdge(&FNodes[NodeIndexA], &FNodes[NodeIndexB], Weight));
}

int TGraph::WeightMinimumSpanningTree()
{
	std::sort(FEdges.begin(), FEdges.end());
	unsigned int TreeCount = 0;
	int Weight = 0;
	for(std::vector<TEdge>::iterator It = FEdges.begin(); It != FEdges.end() && TreeCount < FNodes.size() - 1; ++It){
		if(It->ToMekeCycle()) continue;
		It->JoinTree(TreeCount + 1);
		Weight += It->Weight();
		++TreeCount;
	}
	return Weight;
}

int main()
{
	int NodeCount;
	std::cin >> NodeCount;
	TGraph Graph(NodeCount);
	
	for(int i = 0; i < NodeCount; ++i)
	{
		for(int j = 0; j < NodeCount; ++j){
			int Weight;
			std::cin >> Weight;
			Graph.AddEdge(i, j, Weight);
		}
	}
	
	std::cout << Graph.WeightMinimumSpanningTree() << std::endl;
	return 0;
}

C++: #include <iostream>
#include <cstring>
using namespace std;
#define int long long

main(){
  int n;
  cin>>n;
  int a[n][n];
  for(int i=0;i<n;i++)
    for(int j=0;j<n;j++)
      cin>>a[i][j];
  int ans=0;
  bool used[n];
  memset(used,0,sizeof(used));
  used[0]=1;
  int cost[n];
  for(int i=0;i<n;i++) cost[i]=a[0][i];
  while(1){
    int v=-1;
    for(int i=0;i<n;i++){
      if(used[i]||cost[i]<0) continue;
      if(v<0||cost[i]<cost[v]) v=i;
    }
    if(v<0) break;
    used[v]=1;
    ans+=cost[v];
    for(int i=0;i<n;i++){
      if(a[v][i]<0) continue;
      if(cost[i]<0||a[v][i]<cost[i]) cost[i]=a[v][i];
    }
  }
  cout<<ans<<endl;
}

C++: #include<iostream>
#include<list>
#include<vector>
const int INF = 2001;
using namespace std;
list<int> L;
bool ok(int i) {
    for (list<int>::iterator it = L.begin(); it != L.end(); it++) if (i == *it) return 0;
    return 1;
}
int main() {
    L.push_back(0);
    int n; cin >> n;
    int M[100][100];
    int tmp = INF;
    int id = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> M[i][j];
            if (i == 0 && M[i][j] != -1) {
                if (M[i][j] < tmp) {
                    tmp = M[i][j];
                    id = j;
                }
            }
        }
    }
    L.push_back(id);
    int ans = tmp;
    tmp = INF;
    int OK[100];
    while (1) {
        tmp = INF;
        for (int i = 0; i < n; i++) OK[i] = ok(i); //reached?
        for (list<int>::iterator it = L.begin(); it != L.end(); it++ ) { //from reached
            for (int i = 0; i < n; i++) {
                if (M[*it][i] < tmp && M[*it][i] != -1 && OK[i]) {
                    tmp = M[*it][i];
                    id = i;
                }
            }
        }
        if (tmp == INF) break;
        ans += tmp;
        L.push_back(id);
    }
    cout << ans << endl;
    return 0;
    
}