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 <bits/stdc++.h>
#define rep(i,a) for(i=0;i<a;i++)
using namespace std;
static const int W = 0;
static const int G = 1;
static const int B = 2;

void prim(int n, int &total,vector<vector<int> > &M) {
    int i,u,min;
    vector<int> d(n);
    vector<int> p(n);
    vector<int> color(n);

    rep(i,n){
        d[i] = (1<<21);
        p[i] = -1;
        color[i] = W;
    }
    d[0] = 0;
    while(true){
        min = (1<<21);
        u = -1;
        rep(i,n){
            if(min > d[i] && color[i] != B) {
                u = i;
                min = d[i];
            }
        }
        if(u==-1) break;
        color[u] = B;
        rep(i,n){
            if(color[i] != B && M[u][i]){
                if(d[i] > M[u][i]) {
                    d[i] = M[u][i];
                    p[i] = u;
                    color[i] = G;
                }
            }
        }
    }
    rep(i,n){
        if(p[i] != -1) total += M[i][p[i]];
    }
}

int main(void) {
    int i,j,n,total = 0;
    vector<vector<int> > M;
    cin >> n;
    M.resize(n);

    rep(i,n){
        M[i].resize(n);
    }
    rep(i,n){
        rep(j,n){
            cin >> M[i][j];
            if(M[i][j] == -1) M[i][j] = (1<<21);
        }
    }
    prim(n,total,M);
    cout << total << endl;
    return 0;
}

C++: #include <iostream>
#include <string>
#include <algorithm>
#include <cstdio>
#include <vector>
#include <queue>
#include <set>
#include <numeric>
#include <cmath>

using namespace std;

typedef long long int lld;

const lld mod = 1e9+7;
const lld INF = 1e9;
//const lld MAXN = 1e9;

struct edge
{
	int cost,u,v;
	bool operator<(const edge& e) const
	{
		return cost < e.cost;
	}
};

int main()
{
	int n,a[100][100] = {0};

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

	vector<edge>  e;

	for(int i = 0; i < n; i++)
	{
		for(int j = i; j < n; j++)
		{
			if (a[i][j] >= 0)
			{
				edge f;
				f.cost = a[i][j];
				f.u = i;
				f.v = j;
				e.push_back(f);
			}
		}
	}

	sort(e.begin(),e.end());

	set<int> span;
	int sol = 0;

	for(int i = 0; i < e.size(); i++)
	{
		if (!span.count(e[i].u) || !span.count(e[i].v))
		{
			sol += e[i].cost;
			span.insert(e[i].u);
			span.insert(e[i].v);
		}
	}

	cout << sol << endl;

	return 0;
}

C++: //Minimu Spanning Tree
#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];

long prim(){
    int u, minv;
    int d[MAX], p[MAX], color[MAX];
    
    //d is INF, p is -1, color IS WHITE;
    for(int i = 0; i < n; i++){
        d[i] = INF;
        p[i] = -1;
        color[i] = WHITE;
    }
    //cost of start point is zero.
    d[0] = 0;
    
    while(true){
        minv = INF;
        u = -1;
        
        //????°???¨????????????V - S????????¢???????????????S?????£??\??????????????????
        for(int i = 0; i < n; i++){
            if(minv > d[i] && color[i] != BLACK){
                minv = d[i];
                u = i;
            }
        }
        
        //???????????????????????¨????????????????????????S=V??¨?????£???
        if(u == -1) break;
        
        color[u] = BLACK;
        for(int v = 0; v < n; v++){
            if(color[v] != BLACK && M[u][v]){
                if(M[u][v] < d[v]){
                    d[v] = M[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }
    
    long sum = 0;
    for(int i = 0; i < n; i++){
        if(p[i] != -1) sum += M[i][p[i]];
    }
    
    return sum;
    
}

int main(void){
    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 <sstream>
#include <cstdio>
#include <cmath>
#include <cctype>
#include <string>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>
#include <functional>

using namespace std;
using ll = long long int;
#define rep(i,n) for(int i = 0; i < n; i++)
#define FOR(i, a, b)  for(int i = (a); i < (b) ; i++)

#define pb push_back
#define SORT(v,n) sort(v, v+n)
#define ALL(x) (x).begin(),(x).end()
#define debug(x) cerr << #x << ": " << x << '\n'
#define elif else if
#define itn ll
#define int ll
const int INF = 100100100;
const int MOD = (int)1e9 + 7;
const double EPS = 1e-9;
///                →,↑,←,↓,↗,↖,↙,↘
int dx[8] = { 1, 0, -1, 0, 1, -1, -1, 1 };
int dy[8] = { 0, 1, 0, -1, 1, 1, -1, -1 };

static const int MAX = 100;
static const int White = 0;
static const int Gray = 1;
static const int Black = 2;

int n, M[MAX][MAX],color[MAX];

int prim() {
	int d[MAX], p[MAX];
	int i,sum = 0;
	rep(i, n) {
		d[i] = INF;
		p[i] = -1;
		color[i] = White;
	}
	d[0] = 0;
	while (true) {
		int u = -1;
		int minv = INF;
		rep(i, n) {
			if (color[i] != Black && d[i] < minv) {
				minv = d[i];
				u = i;
			}
		}
		if (u == -1)
			break;
		color[u] = Black;
		int v;
		rep(v, n) {
			if (color[v] != Black && M[u][v] != INF) {
				color[v] = Gray;
				d[v] = M[u][v];
				p[v] = u;
			}
		}
	}
	rep(i, n) {
		if (p[i] != -1) {
			sum += M[i][p[i]];
		}
	}
	return sum;
}

signed main() {
	ios::sync_with_stdio(false);
	cin >> n;
	int i,j;
	rep(i, n) {
		rep(j, n) {
			int a;
			cin >> a;
			M[i][j] = (a == -1) ? INF : a;
		}
	}
	cout << prim() << '\n';
	return 0;
}

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;
}