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 <cstdio>
using namespace std;
static const int  N = 100;
static const int  INFTY = (1<<21);
int M[N][N], color[N];
int n, d[N], p[N];
int ans = 0;

int prim()
{
    for (int i = 0; i < n; i++)
    {
        color[i] = -1;
        d[i] = INFTY;
        p[i] = -1;
    } 
    d[0] = 0;
    int u = -1;
    while (true)
    { 
        int mincost = INFTY;
        u = -1;
        for (int i = 0; i < n; i++)
        {
            if (color[i] != 2 && d[i] < mincost)
            { 
                mincost = d[i];
                u = i;
            }  
        } 

        if (mincost == INFTY) break;
        color[u] = 2;
        for (int i = 0; i < n; i++)
        {
            if (color[i] != 2 && M[u][i] != INFTY)
            { 
                if (M[u][i] < d[i])
                { 
                    d[i] = M[u][i];
                    p[i] = u;
                    color[i] = 1;
                }  
            }  
        } 
    }

    for (int i = 0; i < n; i++)
    {
        if (color[i] == 2 && p[i] != -1) ans += M[i][p[i]];

    } 
    return ans;
}

int main()
{
    cin>>n;
    for (int i = 0; i < n; i++)
    {
        for (int j = 0; j < n; j++)
        {
            int a;
            cin>>a;
            if(a != -1) M[i][j] = a;
            else M[i][j] = INFTY;
        }  
    } 
    prim();
    cout<<ans<<endl;    
    return 0;
}

C++: #include<stdio.h>

static const int MAX = 500;
static const int INFTY = (1<<21);

main(){
  int n, i, j, e, sum,M[MAX][MAX]={0};
  int u,minV,INT_MAX,A[MAX]={INFTY},key[MAX]={INFTY};
  /*

    your code


   */

  scanf("%d", &n);
  
  for ( i = 0; i< n; i++ ){
    for ( j = 0; j < n; j++ ){
      scanf("%d", &e);
      M[i][j] = (e==-1)?INFTY:e;
    }
  }
  
  
  while(){
    minV = 
      for(i=1;i<=n;i++){
        if((i < minV) && 

  






















  sum = 0;

  for ( i = 0; i < n; i++ ){
    if ( p[i] != -1 ) sum += M[i][p[]];
  }

  printf("%d\n", sum);

  return 0;
}

C++: #include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;
typedef long long ll;

static const int INF = 1e9;
static const int MAX = 100;

int n;
struct edge{int to, cost;};
typedef pair<int, int> P;

int mincost[MAX];
bool used[MAX];
vector< vector<edge> > A(MAX);

int prim(){
    int to, cost, res = 0;
    priority_queue<P, vector<P>, greater<P>> que;
    fill(mincost, mincost + n, INF);
    fill(used, used + n, false);
    mincost[0] = 0;
    que.push(P(0, 0));

    while(!que.empty()){
        P p = que.top(); que.pop();
        if (used[p.second]) continue;
        used[p.second] = true;

        for (int i = 0; i < A[p.second].size(); i++){
            to = A[p.second][i].to;
            cost = A[p.second][i].cost;
            if (used[to]) continue;
            if (mincost[to] > cost){
                mincost[to] = cost;
                que.push(P(mincost[to], to));
            }
        }
    }
    for (int i = 0; i < n; i++) res += mincost[i];
    return res;
}

int main(){
    cin >> n;
    edge x;
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            scanf("%d", &x.cost);
            x.to = j;
            if (x.cost != -1) A[i].push_back(x);
        }
    }
    cout << prim() << endl;
    return 0;
}

C++: #include <iostream>
#include <cstdlib>
#include <string>
#include <typeinfo>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <stack>
#include <queue>
using namespace std;
static const int WHITE = 0;
static const int GRAY = 1;
static const int BLACK = 2;
static const int INFTY = (1<<21);
static const int MAX =100;

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 <bits/stdc++.h>
using namespace std;

typedef long long ll;

struct Edge {
    ll s,t;
    ll w;
    bool operator < (const Edge& tgt) const {
	return w > tgt.w;
    }
    void dump(){
	cout << s << " --> " << t << " : " << w << endl; 
    }
};

ll Prim(vector<vector<Edge>>& G) {
    const ll V = G.size();
    priority_queue<Edge> edges;
    
    vector<int> used(V,0);
    edges.push( Edge{-1,0,0} );
    ll ans = 0;
    while( edges.size() ) {
	Edge e = edges.top(); edges.pop();

//	assert(used[e.s] == 1);
	if( used[e.t] == 1 ) continue;
	used[e.t] = 1;
//	e.dump();
	ans += e.w;

	for(auto& nxt : G[e.t]) {
	    if( used[nxt.t] == 1 ) continue;
	    edges.push(nxt);
	}
    }
    for(auto& e : used) assert(e == 1);

    return ans;
}


int main () {

    ll V;
    cin >> V;
    vector<vector<Edge>> G(V);

    for(int i=0; i<V; i++) {
	for(int j=0; j<V; j++) {
	    ll w; cin >> w;
	    if( w != -1 ) {
		G[i].push_back( Edge{i,j,w} );
//		G[j].push_back( Edge{j,i,w} );
//		cout << i << " <--> " << j << " : " << w << endl; 
	    }
	}
    }

    ll ans = Prim(G);
    cout << ans << endl;
        
    return 0;
}