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<iostream>
using namespace std;
#define INF  (1<<21)
//int prim(int M[100][100], int n){
int M[100][100];
int prim(int n){
	int u, mincost;
	int color[n], d[n], p[n];
	for(int i=0; i<n; i++){
		color[i]=0;
		d[i]=INF;
		p[i]=-1;
	}
	d[0]=0;
	while(1){
		mincost=INF;
		u=-1;
		for(int i=0; i<n; i++){
			if(mincost>d[i] && color[i]!=2){
				u=i;
				mincost=d[i];
			}
		}
		if(u==-1)
			break;
		color[u]=2;
		for(int v=0; v<n; v++){
			if(color[v]!=2 && M[u][v]!=INF){
				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(){
	int n;
	cin>>n;
	//int M[100][100];
	for(int i=0; i<n; i++){
		for(int j=0; j<n; j++){
			int e;
			cin>>e;
			if(e!=-1)
				M[i][j]=e;
			else
				M[i][j]=INF;
		}
	}
	cout<<prim(n)<<endl;
	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;

typedef pair<int, int> P;
const int M = 1000000007;

int prim_cost(vector<vector<P>> edge) {
    int n = edge.size();
    vector<int> vis(n, 0);
    int c = 0;
    priority_queue<P, vector<P>, greater<P>> q;
    q.push(P(0, 0));
    while (!q.empty()) {
        P p = q.top();
        q.pop();
        if (vis[p.second]) continue;
        vis[p.second] = 1;
        c += p.first;
        for (auto& e : edge[p.second]) {
            if (!vis[e.second]) {
                q.push(P(e.first, e.second));
            }
        }
    }
    return c;
}


int main() {
    int n;
    cin >> n;
    vector<vector<P>> edge(n);
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < n; ++j) {
            int a;
            cin >> a;
            if (a != -1)
                edge[i].push_back(P(a, j));
        }
    }
    cout << prim_cost(edge) << "\n";
    return 0;
}

C++: #include<iostream>
#include<algorithm>
#define wh 0
#define gr 1
#define bl 2
#define inf 2001
#define null (-1)
#define Max 100 
using namespace std;
int color[Max],m[Max][Max];
int d[Max],p[Max],n;
void prim(){
int i,j,u;
	for(i=0;i<n;i++){
	color[i]=wh;
		d[i]=inf;
	}
	d[0]=0;
	p[0]=-1;
	while(true){
	int mincost=inf;
		for(i=0;i<n;i++){
			if(color[i]!=bl && d[i]<mincost){
			mincost=d[i];
				u=i;
			}
		}
		if(mincost==inf)
		break;
		color[u]=bl;
		for(int v=0;v<n;v++){
			if(color[v]!=bl && m[u][v]!=null){
				if(m[u][v]<d[v]){
				d[v]=m[u][v];
					p[v]=u;
					color[v]=gr;
				}
			}
		}
	}
}

main(){
	int i,j;
	cin>>n;
	for(i=0;i<n;i++){
		for(j=0;j<n;j++){
	cin>>m[i][j];
			m[j][i]=m[i][j];
		}
	}
	prim();
	int ans=0;
	for(i=0;i<n;i++)
	ans+=d[i];
	cout<<ans<<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;
static const int GRAY = 1;
static const int BLACK = 2;

struct Node{
  int color, dist, parent;
};

int n, M[MAX][MAX];
Node node[MAX];

void Printnodes(){
  string col[3] = {"WHITE", "GRAY ", "BLACK"};
  for(int i = 0; i < n; i++){
    cout << "nodeID : " << i ;
    cout << " color : " << col[node[i].color];
    cout << " parent : " << node[i].parent;
    cout << " dist : " << node[i].dist << endl;
  }
  cout << endl;
}

int main(){
  cin >> n;

  for(int i = 0; i < n; i++){
    for(int j = 0; j < n; j++){
      cin >> M[i][j];
    }
    node[i].color = WHITE;
    node[i].dist = INFTY;
    node[i].parent = -1;
  }

  int p = 0;
  node[p].dist = 0;

  while(true){
    //Printnodes();

    for(int i = 0; i < n; i++){
      if(M[p][i] >= 0 && node[i].color != BLACK){
        if(node[i].dist > M[p][i]){
          node[i].dist = M[p][i];
          node[i].parent = p;
          node[i].color = GRAY;
        }
      }
    }

    int min_d = INFTY;
    p = -1;
    for(int i = 0; i < n; i++){
      if(node[i].dist < min_d && node[i].color != BLACK){
        min_d = node[i].dist;
        p = i;
      }
    }

    if(p == -1)
      break;

    node[p].color = BLACK;
    //cout << "node " << p << " turns to BLACK!" << endl;
  }

  int sum = 0;
  for(int i = 0; i < n; i++){
    if(node[i].parent != -1)
      sum += M[i][node[i].parent];
  }
  cout << sum << endl;
  return 0;
}

C++: #include <iostream>
#include <vector>
#include <queue>
#define to first
#define cost second
const int inf=1e9+7;
using namespace std;
int main(){

  int n,tmp,r=0,flag[100]={},v=0;
  cin>>n;
  vector <pair<int,int> > gl[n];
  priority_queue <pair<int,int> ,vector<pair<int,int> >, greater<pair<int,int> > >q;
  //for(int i=1;i<n;i++) mincost[i]=inf;                                                                                                                                                       

  for(int i=0;i<n;i++) for(int j=0;j<n&&cin>>tmp;j++) if(tmp!=-1) gl[i].push_back(make_pair(j,tmp));
  int now=0;
  for(int j=0;j<n-1;j++){
    for(int i=0;i<gl[now].size();i++) if(!flag[gl[now][i].to]) q.push(make_pair(gl[now][i].cost,gl[now][i].to));
    flag[now]=1;
    // cout<<now<<" "<<q.top().first<<endl;                                                                                                                                                    
    for(;flag[q.top().second]||q.empty();) q.pop();
    if(q.empty()) break;
    r+=q.top().first;
    now=q.top().second;
    q.pop();
  }
  cout<<r<<endl;
  return 0;

}

C++: #include <bits/stdc++.h>
using namespace std;
typedef long long ll;

enum state { New, Working, Done };

int main()
{
	int n;
	cin >> n;
	vector<vector<int>> am(n, vector<int>(n));
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) cin >> am[i][j];
	}

	vector<int> d(n, INT_MAX), p(n, INT_MAX);
	vector<state> status(n);
	d[0] = 0;
	p[0] = -1;
	status[0] = Working;
	while (true) {
		int minv = INT_MAX;
		int node = -1;
		for (int i = 0; i < n; i++) {
			if (d[i] < minv && status[i] != Done) {
				minv = d[i];
				node = i;
			}
		}
		if (node == -1) break;
		status[node] = Done;
		for (int i = 0; i < n; i++) {
			if (am[node][i] != -1 && am[node][i] < d[i] && status[i] != Done) {
				d[i] = am[node][i];
				p[i] = node;
				status[i] = Working;
			}
		}
	}
	cout << accumulate(d.begin(), d.end(), 0) << endl;
}