Go: package main

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

const (
	WHITE int = iota
	GRAY
	BLACK
)

type graph struct {
	G [][]int
	C []int
	D []int
	P []int
}

var INFTY = 1 << 32

func constructGraph() *graph {
	sc := bufio.NewScanner(os.Stdin)
	sc.Scan()
	n, _ := strconv.Atoi(sc.Text())

	g := make([][]int, n)
	c := make([]int, n)
	d := make([]int, n)
	p := make([]int, n)

	for i := 0; i < n; i++ {
		sc.Scan()
		fields := strings.Fields(sc.Text())
		g[i] = toIntSlice(fields)
	}

	return &graph{g, c, d, p}
}

func (g *graph) initMst() {
	for i := 0; i < len(g.G); i++ {
		g.C[i] = WHITE
		g.D[i] = INFTY
	}
	g.D[0] = 0
	g.P[0] = -1
}

func (g *graph) primMst() int {
	g.initMst()

	var u int
	for {
		mincost := INFTY
		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.D[i] < mincost {
				mincost = g.D[i]
				u = i
			}
		}

		if mincost == INFTY {
			break
		}

		g.C[u] = BLACK

		for i := 0; i < len(g.G); i++ {
			if g.C[i] != BLACK && g.existEdge(u, i) {
				if g.G[u][i] < g.D[i] {
					g.D[i] = g.G[u][i]
					g.P[i] = u
				}
			}
		}
	}

	totalCost := 0
	for _, cost := range g.D {
		totalCost += cost
	}
	return totalCost
}

func (g *graph) existEdge(u, v int) bool {
	return g.G[u][v] != INFTY && g.G[v][u] != INFTY
}

func toIntSlice(s []string) []int {
	a := make([]int, len(s))
	for i, v := range s {
		num, _ := strconv.Atoi(v)
		if num == -1 {
			num = INFTY
		}
		a[i] = num
	}
	return a
}

func main() {
	g := constructGraph()
	fmt.Println(g.primMst())
}

C++: #include <cstdio>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>

#define N 100
#define INF 0x7FFFFFFF

int prim(std::unordered_map<int, int> a[N], const int n){
    std::unordered_set<int> checked;
    int total = 0;
    checked.insert(0);
    while(checked.size() != n){
        int newId = INF;
        int newWeight = INF;
        for(auto &x: checked){
            for(auto &j: a[x]){
                if(checked.find(j.first) == checked.end() && newWeight > j.second){
                    newId = j.first;
                    newWeight = j.second;
                }
            }
        }
        checked.insert(newId);
        total += newWeight;
    }
    return total;
}

int main(){
    int n;
    std::scanf("%d", &n);
    std::unordered_map<int, int> a[N];
    for(int i = 0; i < n; ++i){
        for(int j = 0; j < n; ++j){
            int v;
            std::scanf("%d", &v);
            if(v != -1){
                a[i].insert(std::make_pair(j, v));
            }
        }
    }
    int val = prim(a, n);
    std::printf("%d\n", val);
    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, A[MAX][MAX];

int prim(){
    int u, minv;
    int d[MAX], p[MAX], color[MAX];

    for(int i = 0; i < n; i++){
        color[i] = WHITE;
        d[i] = INFTY;
    }
    d[0] = 0;
    p[0] = -1;

    while(1){
        minv = INFTY;
        for(int i = 0; i < n; i++){
            if(color[i] != BLACK && d[i] < minv){
                minv = d[i];
                u = i;
            }
        }

        if(minv == INFTY) break;

        color[u] = BLACK;

        for(int v = 0; v < n; v++){
            if(color[v] != BLACK && A[u][v] != INFTY){
                if(A[u][v] < d[v]){
                    d[v] = A[u][v];
                    p[v] = u;
                    color[v] = GRAY;
                }
            }
        }
    }

    int sum = 0;
    for(int i = 0; i < n; i++){
        sum += d[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;
            A[i][j] = (e == -1) ? INFTY : e;
        }
    }

    cout << prim() << endl;

    return 0;
}

C++: #include<bits/stdc++.h>
//cout<<setprecision(1)<<fixed<<endl;
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int MAX_N=100000;
#define eps 1e-7
//#define Kongxiangzhouye

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 begin[10000];
int to[10000];
int next[10000];
int weight[10000];
int e,n;
void add(int x,int y,int z){
	to[++e]=y;
	next[e]=begin[x];
	begin[x]=e;
	weight[e]=z;
}

struct p{
	int edge;
	int weight;
	bool operator < (const p& u)const{
		return weight>u.weight;
	}
};
int createtree(){
	priority_queue<p> q;
	int flag[100];
	memset(flag,0,sizeof(flag));
	int te=begin[1];
	while(to[te]!=-1){
		if(flag[to[te]]==0)
			q.push((p){te,weight[te]});
		te=next[te];
	}
	flag[1]=1;
	int ans=0;
	while(1){
		int flag2=1;
		for(int i=1;i<=n;i++){
			if(flag[i]==0){
				flag2=0;
				break;
			}
		}
		if(flag2==1)
			break;
		while(flag[to[q.top().edge]]==1)
			q.pop();
		p now=q.top();
		q.pop();
		ans=ans+now.weight;
		flag[to[now.edge]]=1;
		int te=begin[to[now.edge]];
		while(te!=-1){
			if(flag[to[te]]==0)
				q.push((p){te,weight[te]});
			te=next[te];
		}
	}
	return ans;
}
int main(){
	ios::sync_with_stdio(false);
	#ifdef Kongxiangzhouye
		freopen("in.txt","r",stdin);
		freopen("out.txt","w",stdout);
	#endif
	while(cin>>n){
		memset(begin,-1,sizeof(begin));
		memset(next,-1,sizeof(next));
		memset(to,-1,sizeof(to));
		e=0;
		for(int i=1;i<=n;i++){
			for(int j=1;j<=n;j++){
				int te;
				cin>>te;
				if(te!=-1)
					add(i,j,te);
			}
		}
		cout<<createtree()<<endl;
	}

	return 0;
}

C++: #include <iostream>
#include <iomanip>
#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <functional>
#include <sstream>
#include <string>
#include <utility>
#include <map>
#include <memory>
#include <set>
#include <vector>
#include <deque>
#include <list>
#include <stack>
#include <queue>
// #include <array>

using namespace std;

class MSTree
{
public:
  int solve();
};

int MSTree::solve()
{
  int n;
  cin >> n;
  
  vector<vector<int>> adj(n, vector<int>(n));
  list<int> t, vt;

  for ( auto i = 0; i < n; ++i )
    for ( auto j = 0; j < n; ++j )
      cin >> adj[i][j];

  t.push_back( 0 );

  for ( auto i = 1; i < n; ++i )
    vt.push_back( i );

  int w = 0;

  while ( vt.size() )
    {
      int mw = 4000;
      list<int>::iterator itm;
      
      for ( auto ita = t.begin(); ita != t.end(); ++ita )
        for ( auto itb = vt.begin(); itb != vt.end(); ++itb )
          {
            if ( adj[*ita][*itb] >= 0 && mw > adj[*ita][*itb] )
              {
                itm = itb;
                mw = adj[*ita][*itb];
              }
          }
      
      w += mw;
      t.push_back( *itm );
      vt.erase( itm );
    }

  cout << w << endl;
    
  return 0;
}

int main()
{
  MSTree m;

  m.solve();

  return 0;
}