Thread: Remove a number from a stack

Hello! I am pretty new to java, so pleasee be patient with me !!

Ok, so I am trying to remove a value from a stack that is not in the top of the stack using only stacks, so I basically created 2 stacks pila and pilaTemp and move values from one another and then push back the values a move to the second stack, not sure if I explain my self, but anyways here is the code. I have a problem with the loops I think, but I've been trying to understand what I am doing wrong but nothing comes to my mind, and what I try does not work. For example.. I am able to remove the top value (32).. but if I want to remove 3, it won't do anything! If anyone can send me in the right direction I'll appreciate it! thanks!!

Here is the code:

 
public class Pila {
 
    Stack<Integer> pila = new Stack<>();
    Stack<Integer> pilaTemp = new Stack<>();
    //Stack<Integer> pilaDestino = new Stack<>();
 
 
    public void Pila() {
        pila.push(4);
        pila.push(20);
        pila.push(25);
        pila.push(3);
        pila.push(32);
    }
 
  public void sacaNumero(int n){
 
      for(int i = 0; i<pila.size(); i++){
 
        if(pila.peek()== n){
          pila.pop();
            } else if(pila.peek()!= n){
                do{
                pilaTemp.push(pila.pop());
                    if(pila.peek() == n)
                    pila.pop();
                    pila.push(pilaTemp.pop());
 
            } while(pila.peek() != n && pila != null);
 
      }  else if(pila.isEmpty() || pila.search(n) == -1){
          System.out.print("No se puede completar la acción. El número no existe o la pila está vacía");
      }
        System.out.print(pila);
      }
  }

The do/while loop in the sacaNumero() method is an infinite loop. You can verify this by adding a print statement inside the loop somewhere. You might try writing down the steps to find the desired item in the stack, discard it, and then rebuild the original stack without it in your native language - maybe in code comments (novel idea) - and then code that.

Hi Greg!

Ok! I understand what you are saying and trust you that it is an infinite loop (no wonder why the CPU usage is 100% haha), I thought that while (pila.peek() != n || pila.isEmpty()) this was the stop. I mean I want it to go through the whole stack (pila) and do the pila.pop() and push that value into pilaTemp (temporary stack). I mean it is just four values and I trying to access the second one (#3) so in my head it should stop when 3 = 3. It is obviously wrong, but I just can't see it, it's frustrating! Is this a normal feeling when you begin programming? hehe

Again, I think writing down the steps would be helpful. As a hint, your current code is much more complicated than it needs to be. I suggest you start that method over from a blank sheet of paper, beginning with the list of steps before writing any code.

Hi Greg!
I was able to do it as you said, I built my stack without the usage of collections and worked great! Thanks for the tip, drafting it in paper worked for me.

I am now having an issue with queues... I was able to built my queue and it works fine, however I have an issue, I´ve been trying to change to my loops but I always get the same result... I want to remove a number from my queque maintaining the queue order, I am able to remove the number, but I am not able to maintain the order of it, can you help me with it? I should be removing the name and continue moving my queue to my aux queue but it is not happening that.. Ive tried different ways but I always get the same result.. not sure how to make it continue.

 
public NodoC extrae(int x, Cola fuente) {
 
        NodoC retorno = null; 
        Cola aux = new Cola(); 
        NodoC n = fuente.atiende(); 
 
        while (n != null && retorno == null) { 
            if (n.getDato() == x) { 
 
                retorno = n;
            } else {
                aux.encola(n);           
                n = fuente.atiende();
            }
        }
 
        n = aux.atiende();
        while (n != null) {
            fuente.encola(n);
            n = aux.atiende();
        }
        return retorno;
    }