Go: package main

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

const BIG_COST = 3000

const (
	ST_NOT_YET = iota
	ST_JOINED
)

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	nNodes := scanInt(sc)
	costs := make([][]int, nNodes)

	for r := 0; r < nNodes; r++ {
		costs[r] = make([]int, nNodes)
		for c := 0; c < nNodes; c++ {
			costs[r][c] = scanInt(sc)
		}
	}

	states := make([]int, nNodes)
	minCosts := make([]int, nNodes)

	for i := 1; i < nNodes; i++ {
		minCosts[i] = BIG_COST
	}

	for {
		var u int
		minCost := BIG_COST

		for i := 0; i < nNodes; i++ {
			if states[i] != ST_JOINED && minCosts[i] < minCost {
				minCost = minCosts[i]
				u = i
			}
		}

		// 全てのノードが MST に JOIN できたので終了。
		if minCost == BIG_COST {
			break
		}

		states[u] = ST_JOINED

		for v := 0; v < nNodes; v++ {
			cost := costs[u][v]

			// MST内の u と MST外の v との辺の重みをそれぞれ minCosts[v] として
			// 保存しておく。このうち辺の重みが最小となる v が次のループで MST に JOIN する。
			if states[v] != ST_JOINED && cost != -1 && cost < minCosts[v] {
				minCosts[v] = cost
			}
		}
	}

	sum := 0
	for _, cost := range minCosts {
		sum += cost
	}
	fmt.Println(sum)
}

func scanInt(sc *bufio.Scanner) int {
	sc.Scan()
	v, _ := strconv.Atoi(sc.Text())
	return v
}

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

constexpr int INF = 3000;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    int n, aij, mincost, minu, sum=0;
    std::cin >> n;
    std::vector<std::vector<int>> a(n);
    std::vector<int> d(n), p(n), color(n); // white:0, gray:1, black:2
    for (int i=0; i<n; i++) {
        for (int j=0; j<n; j++) {
            std::cin >> aij;
            a[i].push_back(aij);
        }
        d[i] = INF;
    }
    d[0]=0;
    p[0]=-1;
    while (true) {
        mincost = INF;
        for (int i=0; i<n; i++) {
            if (color[i] < 2 and d[i] < mincost) {
                mincost = d[i];
                minu = i;
            }
        }
        if (mincost == INF) {
            break;
        }
        color[minu] = 2;
        for (int v=0; v<n; v++) {
            if (color[v] < 2 and a[minu][v] >= 0 and d[v] > a[minu][v]) {
                d[v] = a[minu][v];
                p[v] = minu;
                color[v] = 1;
            }
        }
    }

    for (int i=0; i<n; i++) {
        sum += d[i];
    }
    std::cout << sum << "\n";

    return 0;
}

C++: #include <stdio.h>
#define rep(i, n) for(int i = 0; i < n; ++i)

int main(void) {
  int n, i, j, ans = 0;
  scanf("%d", &n);
  int a[n][n];
  char f[n];
  rep(i, n) rep(j, n) scanf("%d", &a[i][j]);
  rep(i, n) f[i] = 0;
  f[0] = 1;
  rep(i, n - 1) {
    int min = 10000, minx, miny;
    rep(j, n) {
      rep(k, n) {
        if(f[j] && !f[k] && a[j][k] > 0 && a[j][k] < min) min = a[j][k], minx = j, miny = k;
      }
    }
    ans += min;
    f[miny] = 1;
  }
  printf("%d\n", ans);
  return 0;
}

C++: #include <iostream>
#include <queue>
#include <utility>
#include <functional>
#include <vector>
using namespace std;
int cost[100][100];
int prim(int n,int s){
	typedef pair<int,int> P;
	bool ischeck[n];
	int mincost = 0;
	priority_queue<P,vector<P>,greater<P> > pq;
	P p,tp;
	for(int i = 0;i < n;++i){
		ischeck[i] = false;
		if(cost[s][i] != -1){
			p.first = cost[s][i];
			p.second = i;
			pq.push(p);
		}
	}
	ischeck[s] = true;
	while(!pq.empty()){
		p = pq.top();
		pq.pop();
		if(ischeck[p.second]) continue;
		else{
			ischeck[p.second] = true;
			mincost += p.first;
			for(int i = 0;i < n;++i){
				if(cost[p.second][i] != -1){
					tp.first = cost[p.second][i];
					tp.second = i;
					pq.push(tp);
				}
			}
		}
	}
	return mincost;
}
int main(){
	int n;
	cin >> n;
	for(int i = 0;i < n;++i){
		for(int j = 0;j < n;++j){
			cin >> cost[i][j];
		}
	}
	cout << prim(n,0) << endl;
}

C++: #include <stdio.h>
#include <limits.h>
int n,M[100][100];
int prim();
int main(){
  int i,j,w;
  scanf("%d",&n);
  for(i=0;i<n;i++){
    for(j=0;j<n;j++){
      scanf("%d",&w);
      if(w==-1)M[i][j]=INT_MAX;
      else M[i][j]=w;
    }
  }
  printf("%d\n",prim());
  return 0;
}
int prim(){
  int sum,i,u,mincost,C[100],d[100],p[100];
  for(i=0;i<n;i++){
    d[i]=INT_MAX;
    C[i]=0;
    p[i]=-1;
  }
  d[0]=0;
  while(1){
    u=-1;
    mincost=INT_MAX;
    for(i=0;i<n;i++){
      if(C[i]!=2&&d[i]<mincost){
        mincost=d[i];
        u=i;
      }
    }
    if(u==-1)break;
    C[u]=2;
    for(i=0;i<n;i++){
      if(C[i]!=2&&M[u][i]!=INT_MAX){
        if(d[i]>M[u][i]){
          d[i]=M[u][i];
          p[i]=u;
          C[i]=1;
        }
      }
    }
  }
  sum=0;
  for(i=0;i<n;i++){
    if(p[i]!=-1)sum+=M[i][p[i]];
  }
  return sum;
}

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

class TEdge;
struct TNode
{
	int TreeIndex;
	std::set<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::set<const TEdge*>::const_iterator It = Connected.begin(); It != Connected.end(); ++It){
		(*It)->JoinTree(Index);
	}
	Connected.insert(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;
}