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;
static const int MAX=101;
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 i=0;i<n;i++){
            if(color[i]!=BLACK && M[u][i]!=INFTY){
                if(d[i]>M[u][i]){
                    d[i]=M[u][i];
                    p[i]=u;
                    color[i]=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++){
            cin >> M[i][j];
            if(M[i][j]==-1) M[i][j]=INFTY;
        }
    }
    
    cout << prim() << endl;
    
    return 0;
}

C++: #include <iostream>
using namespace std;
static const int MAX = 100;
static const int INFTY = (1 << 21);
static const int NOT_VISIT = 0;
static const int VISITING = 1;
static const int VISITED = 2;
int n;
int M[MAX][MAX];
int prim()
{
    int minv, u;
    int isVisited[MAX], d[MAX], p[MAX];
    for (int i = 0; i < n; i++) {
	isVisited[i] = NOT_VISIT;
	d[i] = INFTY;
	cout << "d[i]: " << d[i] << endl;
	p[i] = -1;
    }
    d[0] = 0;
    while (1) {
	minv = INFTY;
	cout << "minv: " << minv << endl;
	u = -1;
	for (int i = 0; i < n; i++) {
	    if (minv > d[i] && isVisited[i] != VISITED) {
		u = i;
		minv = d[i];
	    }
	}
	if (u == -1) {
	    break;
	}

	isVisited[u] = VISITED;
	for (int j = 0; j < n; j++) {
	    if (isVisited[j] != VISITED && M[u][j] != INFTY) {
		if (d[j] > M[u][j]) {
		    d[j] = M[u][j];
		    p[j] = u;
		    isVisited[j] = VISITING;
		}
	    }
	}
    }
    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;
}

C++: #define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES
//#include "MyMath.h"
//#include "MyDisjointset.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <functional>
#include <stdio.h>
using namespace std;
typedef pair<int, int> P;
const int INF = 2000000000;
int main() {
	int n; cin >> n;
	int m[101][101];
	for (int i = 0; i < n; i++)for (int j = 0; j < n; j++)
		cin >> m[i][j];
	int res = 0;
	int *d = new int[n];
	fill(d, d + n, INF); 
	d[0] = 0;
	bool *visit = new bool [n];
	fill(visit, visit + n, false);
	priority_queue <P, vector<P>, greater<P> > q;
	q.push(P(d[0], 0));
	while (!q.empty()) {
		int f = q.top().first, s = q.top().second;
		visit[s] = true;
		res += f;
		q.pop();
		for (int i = 0; i < n; i++)
			if (!visit[i] && m[s][i] != -1 && d[s] > d[i] + m[s][i]) {
				d[s] = d[i] + m[s][i];
				q.push(P(d[i], i));
			}
	}
	cout << res << endl;
	delete[] d, visit;
	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
int prim(void);

#define MAX 100
#define WHITE 0
#define GRAY 1
#define BLACK 2

int A[MAX][MAX];
int n;

int main(){
  int i,j,e;
  int u;
  cin >> n;
  for(i = 0; i < n; i++){
    for(j = 0; j < n; j++){
      cin >> e;
      A[i][j] = (e == -1) ? INFINITY : e;
    }
  }
  cout << prim() << endl;
  return 0;
}

int prim(){
  int sum = 0;
  int i,j,minV;
  int d[MAX],p[MAX],color[MAX];
  int u,v; 
  for(i = 0; i < n; i++){
    d[i] = INFINITY;
    p[i] = -1;
    color[i] = WHITE;
  }
  d[0] = 0;
  while(1){
    minV = INFINITY;
    u = -1;
    for(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(v = 0; v < n; v++){
      if(color[v] != BLACK && A[u][v] != INFINITY){
        if(d[v] > A[u][v]){
          d[v] = A[u][v];
          p[v] = u;
          color[v] = GRAY;
        }
      }
    }
  }
  //sum = 0;
  for(i = 0; i < n; i++){
    if(p[i] != -1){
      sum += A[i][p[i]];
    }
  }
  return sum;
}

C++: #include <climits>
#include <iostream>
using namespace std;

#define MAX_N 2000
int n;
int A[MAX_N][MAX_N];

class Node
{
    public:
        int cost = INT_MAX;;
        bool used = false;
};

int prim()
{
    int i, u, v, minv, sum = 0;
    Node *nodes = new Node[n];
    nodes[0].cost = 0;
    while (true) {
        u = -1; minv = INT_MAX;
        for (i = 0; i < n; i++) {
            if (nodes[i].cost < minv && !nodes[i].used) {
                u    = i;
                minv = nodes[i].cost;
            }
        }
        if (-1 == u) break;
        nodes[u].used = true;
        sum += nodes[u].cost;
        for (v = 0; v < n; v++) {
            if (!nodes[v].used && A[u][v] != -1) {
                nodes[v].cost = A[u][v] < nodes[v].cost ? A[u][v] : nodes[v].cost;
            }
        }
    }
    return sum;
}

int main()
{
    cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> A[i][j];
        }
    }
    cout << prim() << endl;
    return 0;
}