Go: package main

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

func getScanner(fp *os.File) *bufio.Scanner {
	scanner := bufio.NewScanner(fp)
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 500001), 500000)
	return scanner
}

func getNextString(scanner *bufio.Scanner) string {
	scanner.Scan()
	return scanner.Text()
}

func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}

func main() {
	fp := os.Stdin
	if len(os.Args) > 1 {
		fp, _ = os.Open(os.Args[1])
	}

	scanner := getScanner(fp)
	writer := bufio.NewWriter(os.Stdout)

	n := getNextInt(scanner)

	g := make([][]int, n)
	ans := make([][]int, n)

	inf := 1 << 30
	for i := 0; i < n; i++ {
		g[i] = make([]int, n)
		ans[i] = make([]int, n)
		for ii := 0; ii < n; ii++ {
			g[i][ii] = getNextInt(scanner)
			if g[i][ii] == -1 {
				g[i][ii] = inf
			}
			ans[i][ii] = -1
		}
	}

	im := make(IntMap, 1)

	im.increment(1)

	for len(im) < n {
		min := inf
		u := -1
		v := -1
		for i := range im {
			for ii := 0; ii < n; ii++ {
				if im.get(ii) != 0 {
					continue
				}
				if min > g[i][ii] {
					min = g[i][ii]
					u = i
					v = ii
				}
			}
		}
		im.increment(v)
		ans[u][v] = min
		ans[v][u] = min
	}

	sum := 0
	for i := 0; i < n-1; i++ {
		for ii := i + 1; ii < n; ii++ {
			if ans[i][ii] != -1 {
				sum += ans[i][ii]
			}
		}
	}

	fmt.Fprintln(writer, sum)
	writer.Flush()
}

// IntMap ...
type IntMap map[int]int

func (m IntMap) get(key int) int {
	if _, ok := m[key]; ok {
		return m[key]
	}
	return 0
}
func (m IntMap) increment(key int) {
	if _, ok := m[key]; ok == false {
		m[key] = 0
	}
	m[key]++
}

C++: #include<iostream>
#include<stdio.h>
using namespace std;
static const int INFTY = (1 << 21);

int n, m[100][100];

int prim() {
    int u, minv;
    int d[100], p[100], color[100];
    
    for (int i = 0; i < n; i++) {
        d[i] = INFTY;
        p[i] = -1;
        color[i] = 0;
    }
    
    d[0] = 0;
    
    while(1) {
        minv = INFTY;
        u = -1;
        for (int i = 0; i < n; i++) {
            if (minv > d[i] && color[i] != 2) {
                u = i;
                minv = d[i];
            }
        }
        if (u == -1) break;
        color[u] = 2;
        for (int v = 0; v < n; v++) {
            if (color[v] != 2 && m[v][u] != INFTY) {
                if (d[v] > m[u][v]) {
                    d[v] = m[u][v];
                    p[v] = u;
                    color[v] = 1;
                }
            }
        }
    }
    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;
            if (e == -1) {
                m[i][j] = INFTY;
            } else {
                m[i][j] = e;
            }
        }
    }
    
    cout << prim() << endl;
    
    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;
}

C++: #include <bits/stdc++.h>

#define REP(i, n) for(int i=0;i<(int)(n);i++)
#define ALL(x) (x).begin(),(x).end()
const int INF = 1e9;

using namespace std;
int n;
int res = 0;
struct node {
    int id;
    int parent;
};

node v[100];
vector<tuple<int, int, int>> cost;
vector<int> path;

int find(node x){
    if(x.parent == -1){
        REP(i, path.size())
            v[path[i]].parent = x.id;
        path.clear();
        return x.id;
    }
    else{
        path.push_back(x.id);
        return find(v[x.parent]);
    }
}

void marge(node x, node y){
    int x_id = find(x);
    int y_id = find(y);
    if(x_id == y_id)
        return;
    else
        v[y_id].parent = x_id;
    return;
}

bool judge(node x, node y){
    vector<int> xpath, ypath;
    return find(x) == find(y);
}

int main() {
    cin >> n;
    REP(i, n) REP(j, n) {
        int tmp;
        cin >> tmp;
        if(tmp != -1)
            cost.push_back(make_tuple(tmp, i, j));
    }
    REP(i, n){
        v[i].id = i;
        v[i].parent = -1;
    }
    sort(ALL(cost));
    REP(i, cost.size()){
        node from = v[get<1>(cost[i])];
        node to = v[get<2>(cost[i])];
        if(judge(from, to)){
            continue;
        }
        res += get<0>(cost[i]);
        marge(from, to);
    }

    cout << res << endl;
    return 0;
}

C++: #include<iostream>

using namespace std;

static const int MAX = 100;
static const int INFTY = (1 << 21);
static const int WHITE = 0, GRAY = 1, 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;
}

C++: #include <stdio.h>
#include <stdlib.h>
#include <iostream>
#define INF 1000000000
#define NUM 100
#define NIL -1
#define WHITE 0
#define BLACK 1
using namespace std;

int G[NUM][NUM];
int V[NUM];
int color[NUM];
int node_num;
int dist_sum = 0;

void init(){
    for(int i = 0; i < node_num; i++){
        for(int j = 0; j < node_num; j++){
            int a;
            scanf("%d", &a);
            if(a == -1){
                G[i][j] = INF;
            }else{
                G[i][j] = a;
            }
        }
    }

    for(int i = 0; i < node_num; i++){
        V[i] = INF;
        color[i] = WHITE;
    }
}

void updateAround(int n){
    color[n] = BLACK;
    for(int i = 0; i < node_num; i++){
        V[i] = min(V[i], G[n][i]);
    }

    int min_index = NIL;
    int min_value = INF;
    for(int i = 0; i < node_num; i++){
        if(color[i] == BLACK){
            continue;
        }
        if(V[i] < min_value){
            min_value = V[i];
            min_index = i;
        }
    }
    if(min_index != NIL){
        dist_sum += min_value;
        updateAround(min_index);
    }
}

int main(void){
    scanf("%d", &node_num);

    init();
    updateAround(0);

    printf("%d\n", dist_sum);
}