 So one of the things I want to ask you now is, what are all of these operations in in-form? Now, if we thought about it, a push and popping and all of these things, what's interesting is each one of them is actually being ran through a constant speed. Now, this depends on your implementation, but if you follow sort of some of the guidelines of a stack, you can make something like push and pop and all of these, only a one. And that's going to be through the magic of variables. There's nothing in the world that says I can't have a variable in place. Let's actually sort of look at just a generic list for a second. Let's say I had 80, 90, 250. Well, actually let's start with just an empty list. I think that might be a better way. So one of the things that we do is if we created this stack sort of class, is we could assign it a few different variables. So I assigned it a size of zero. All right, well, if we think about that, since I happen to have a size variable, then that size operation, all I have to do is return this. And we already remember that a return statement, return size is just o of one, because it only takes one operation. So what happens if, say for our sake, I then came in with a push of one, well, 10. All right, well, this is where things can be a little interesting, because how big is this array, this list that I've created? We don't know right now. And so you're saying, oh, I might have to double this and copy over the array. Now, you see, one of the kind of tricks that we can do is we could create another variable, just like we did here with size. What if I also created something called capacity? And I just gave it some arbitrary value, 10,000. It could be, you know, more or less, doesn't matter. But I gave it 10,000. Well, what that means is I now have 10,000 prearranged slots inside of my array that's being used in this case to handle my stack. So all of a sudden, when I say something like push 10, well, the first thing I do is I look up what size. Well, size happens to be an O in one operation. Let me, there we go. So that's only going to take one. And we put that 10 in, because I've now accessed that point in memory. And then I need to increase size. Size plus plus. Once again, this is a mathematical operation. It's O in of one. And so just like we did here with size, push can stay O of one. All right, well, pop. If we think about using those same two kind of concepts there, pop is going to give me back that 10. It's going to remove that from the list. So, first thing I need to know is what size. Again, I need to know sort of where I am. Size, well, size happens to be that. I also need to do a mathematical equation of that minus one, but that's still one. And then I need to make size one less. As you can imagine, if making it one more is one, size is one. So just like before, pop is one. So we've already started to tackle a few of these. You can imagine that top, I'm going to keep it in the same color. Top is everything but getting rid of size and deleting out the element. So top, we can already just knock out as being one as well. And then finally we're left with that last operation. Is empty. Well, luckily a comparison, say for example, a compare is sun. For our sake, is size equal equal zero. Comparison's no different than a mathematical equation. I take one element, I look at another element, and I do something to those elements. Again, not terribly outlandish. It's a primitive operation, and so we would classify that as one. And so, just like I was saying, every single one of the operations of a stack are then stored as one. Now, before I go, if I happened to need to increase my capacity, that, well, change colors, if I had to increase that capacity, maybe I wanted to double it. That is in that case, O of N, I would have to go in, copy all the elements, to a new list, and iterate through that. And so it would be dependent on that. So that one, yeah, okay. But for the most part, we could just not design that. If your stack's full, your stack's full, throw an error, whatever. But as you can see, pretty much all the others. Oh, that is not what I wanted. All the others, O of one.