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>

using namespace std;
static const int MAX=100;
static const int INF=1<<21;

int p[MAX]; //????°???????????????????????????¶??????
int d[MAX]; //??????????¨??????????????????????????????????????????????
int M[MAX][MAX]; //u???v????????????
bool visited[MAX]; //??????????¢??????\

int prim(int n)
{
    //init
    for(int i=0;i<n;i++)
    {
        p[i]=-1;
        visited[i]=false;
        d[i]=INF; //????§???????????????????d?????????????????§
    }

    d[0]=0; //?¬¬0?????????d?????´??°
    while(true)
    {
        //??????d???????°????????????\??????
        int min=INF;
        int min_point=-1;
        for(int i=0;i<n;i++)
        {
            if(d[i]<min&&visited[i]==false)
            {
                min_point=i;
                min=d[i];
            }
        }
        if(min==INF) break;
        visited[min_point]=true;
        //??´??°???????????°?????\????????????????????????d???
        for(int i=0;i<n;i++)
        {
            if(M[min_point][i]!=INF&&visited[i]==false)
                if(d[i]>M[min_point][i])
                {
                    d[i] = M[min_point][i]; //??????d????????§????°±????????´??°
                    p[i]=min_point; //??????
                }
        }
    }
    int sum=0;
    for(int i=0;i<n;i++)
        if(p[i]!=-1) //??????????°?????????????????????¶
           sum+=M[i][p[i]];
    return sum;
}

int main()
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<n;j++)
        {
            cin>>M[i][j];
            M[i][j]=(M[i][j]==-1?INF:M[i][j]);
        }
    }
    cout<<prim(n)<<endl;
}

C++: #include <iostream>

using namespace std;
int n;
int dat[100][100];
int cost[100];
int done[100];

void prim(){
	for(int i=0;i<n;i++){
		cost[i]=1<<21;
		done[i]=0;
	}
	int s=0;	
	int next, ncost=1<<21;
	done[s]=1;
	cost[s]=0;
	while(1){
		ncost=1<<21;
		for(int j=0;j<n;j++){
			if(done[j]){
				for(int i=0;i<n;i++){
					if(dat[j][i]!=-1){
						if(cost[i]>=dat[j][i]&&!done[i]){
							cost[i]=dat[j][i];
						}
						if(ncost>cost[i]&&!done[i]){
							next=i;
							ncost=cost[i];
						}
					}
				}
			}
		}
//		cout<<"next:"<<next<<" cost:"<<cost[next]<<endl;
		done[next]=1;
		int flag=true;
		for(int i=0;i<n;i++){
			if(!done[i]) flag = false;
		}
		if(flag)
			return;
	}
}


int main(){
	cin>>n;
	for(int i=0;i<n;i++){
		for(int j=0;j<n;j++){
			cin>>dat[i][j];
		}
	}
	prim();
	int sum=0;
	for(int i=0;i<n;i++){
		sum+=cost[i];
	}
	cout<<sum<<endl;
	return 0;
}

C++: #include <algorithm>
#include <iostream>
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;
  else {
    P[a] = root(P[a]);
    return 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;
  pair <int, int> edge[10010];
  for (int i=0; i<N; i++){
    for (int j=0; j<N; j++){
      cin >> edge[i*N+j].first;
      edge[i*N+j].second = i*N+j;
    }
  }
  sort(edge, edge+N*N);
  init(N);
  int ans = 0;
  int b = 0;
  for (int k=0; k<N*N; k++){
    while(edge[k].first < 0) k++;
    int i = edge[k].second / N;
    int j = edge[k].second % N;
    if (is_same_set(i,j)){}
    else{
      unite(i,j);
      ans += edge[k].first;
    }
  }
  cout << ans << endl;
}

C++: #include<bits/stdc++.h>
#define REP(i,n) for(int i=0;i<(int)(n);i++)
using namespace std;

int N;
const int MAX_E=100;
int label[MAX_E];
priority_queue<int,vector<pair<int,pair<int,int> > >,greater<pair<int,pair<int,int> > > > pq;

int main(){
  cin>>N;
  REP(i,N)
    label[i]=i;
  REP(i,N){
    REP(j,N){
      int a;cin>>a;
      if(a>=0&&i>j){
	pq.push(make_pair(a,make_pair(j,i)));
      }
    }
  }
  int size=0;
  while(!pq.empty()){
    int cost=pq.top().first;
    pair<int,int> e=pq.top().second;
    pq.pop();
    if(label[e.first]!=label[e.second]){
      size+=cost;
      REP(i,N){
	if(label[i]==label[e.second])
	  label[i]=label[e.first];
      }
    }
  }
  printf("%d\n",size);
}

C++: #include "stdafx.h"
#include <iostream>
using namespace std;

int main(void)
{
	int n, now = 0, flag[101] = {};
	long ans = 0, an[100][100], min[100];

	cin >> n;

	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++)
			cin >> an[i][j];
		min[i] = 1000000000;
	}

	do {
		long key = LONG_MAX, key_i;
		flag[now] = 1;
		flag[100] = 0;

		for (int i = 0; i < n; i++) {
			if (an[now][i] != -1 && an[now][i] < min[i] && flag[i] == 0)
				min[i] = an[now][i];
			if (flag[i] == 0 && min[i] < key) {
				key = min[i];
				key_i = i;
			}
			if (flag[i] == 1)
				flag[100]++;
		}

		now = key_i;
		ans += key;

	} while (flag[100] != n - 1);

	cout << ans << endl;

	return 0;
}

C++: #include <cstdio>
#include <cstring>
#define MAXN (1 << 21)
int g[101][101], d[101], n;
bool vis[101];

int mst()
{
  int sum = 0;
  d[0] = 0;
  for (int j = 0; j < n; j++)
  {
    int u = -1;
    int mini = MAXN;
    for (int i = 0; i < n; i++) // take node from V-T to T
    {
      if (d[i] < mini && !vis[i])
      {
        u = i;
        mini = d[i];
      }
    }
    if (u == -1) return -1;
    sum += mini;
    vis[u] = true;
    for (int v = 0; v < n; v++) // update smallest weight
    {
      if (!vis[v] && g[u][v] >= 0 && d[v] > g[u][v])
      {
        d[v] = g[u][v];
      }
    }
  }
  return sum;
}

int main()
{
  memset(vis, false, sizeof(vis));
  scanf("%d", &n);
  for (int i = 0; i < n; i++)
  {
    d[i] = MAXN;
  }
  for (int i = 0; i < n; i++)
  {
    for (int j = 0; j < n; j++)
    {
      scanf("%d", &g[i][j]);
    }
  }
  printf("%d\n", mst());
}

C++: #include <iostream>
using namespace std;

#define N 101
#define INF 2010
int n;

int A[N][N];
int color[N];
int d[N];

int mst(int root) {
    int totalW = 0;
    d[root] = 0;

    while(true) {
        int added = -1;
        int minw = INF;
        for (int i = 0; i < n; i++) {
            if (color[i] == 0 && d[i] < minw) {
                added = i;
                minw = d[i];
            }
        }

        if (added == -1) {
            break;
        }

        totalW += minw;
        color[added] = 1;
        for (int i = 0; i < n; i++) {
            if (color[i] == 0 && A[added][i] < d[i]) {
                d[i] = A[added][i];
            }
        }
    }

    return totalW;
}

int main() {
    cin >> n;

    int w;
    for (int i = 0; i < n; i++) {
        color[i] = 0;
        d[i] = INF;
        for (int j = 0; j < n; j++) {
            cin >> w;
            if (w == -1) A[i][j] = INF;
            else A[i][j] = w;
        }
    }

    cout << mst(0) << endl;

    return 0;
}