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In this lecture, we are now going to talk about what a stack is.

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And a stack is something that we have been talking about.

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If you remember when we would say we would unwind the stack when referring to recursion.

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So we were now going to get a better insight as to what a stack actually is.

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So the first thing to know about a stack is there's a specific order in which we can insert and remove

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elements so specific.

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Order in how.

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We insert.

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And remove.

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Elements.

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And now this order actually has its own acronym, and it is called LIFO.

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And LIFO is last in.

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First out.

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Meaning we can insert at.

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The top.

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And then take from the top.

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So think of this as a stack of plates.

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And I like to think of it as a stack of plates, because when you put plates into the cabinet, if you

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add a plate here, well, you're not going to take this plate.

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You're going to take the plate that you recently just add it in.

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So then you would take that plate.

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So last in, first out.

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So when we look at a stack, we'll say that this is our stack.

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We will say push ten.

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Well, now we have ten here.

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And then if we push 20 and now we have 20 here, push 30.

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Now we have 30 here.

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But then if we call Pop.

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Now 30 is gone.

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And then if we push 40, now 40 is here.

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And if we call pop again now 40 is gone.

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So this might seem very similar to something that we just did.

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So let's just so our stack is here.

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Our top is here.

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We insert at the top,

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we remove.

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From the top, so this might seem very familiar.

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We just did something like this with our linked list Every time we put in a new value when we called

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pop, that latest value that we pushed in was removed.

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And that is because you might have guessed it, we implemented a stacked base.

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Linked list.

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So while we were learning Linked List, we were actually implementing a stack as well.

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So that is why we're not going to spend too much time talking about a stack, because while we were

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learning linked lists, we also learned what a stack is and how to implement a stack.

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But.

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A stack does have a counterpart and and its counterpart is a Q.

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So in the next lecture we will go over what a Q is and then we will implement our own Q.