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‫So now we're going to do doubly linked lists and we'll start out by creating our constructor.

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‫So the constructor is going to be very similar to what we saw with a singly linked list, except we're

3
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‫going to be making nodes that also point the other way.

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‫So I'm going to put this back as a singly linked list.

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‫So am I going to look at that singly linked list node which looked like this?

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‫We said that was very similar to an unordered map like this and the constructor looked like this.

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‫So for a doubly linked list, the only change that we need to make is adding a second pointer that will

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‫point at the previous node, and then we'll create a constructor, we'll pass that a value, and then

9
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‫we'll say, this value equals value.

10
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‫This is the same as we did for a singly linked list, or we're passing the constructor of value.

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‫That's what this value is here, and that we set this value to be equal to value and this value.

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‫Is the member variable up here.

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‫So that's how we actually assign that value to a node and then we'll initialize that next and previous

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‫pointer to be equal to null pointer.

15
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‫So now that we've created our node class, let's start creating our doubly linked list class.

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‫So I'm going to start out by creating our member variables.

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‫I'm going to mark these as private.

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‫But this line here is not necessary because everything is private by default.

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‫I just like to do this because I think it makes the code more readable.

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‫To explicitly put this in here.

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‫So just like with singly linked lists, we're going to have head, we're going to have tail and we're

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‫going to have length, and then we'll create our constructor.

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‫The constructor needs to be public and we'll start the constructor out like this.

24
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‫And let's just focus in on that constructor.

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‫So the first thing we'll do with this is create a node.

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‫So notice that this is the exact same line of code that we used in the singly linked list class.

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‫It's just that we're calling a different node class.

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‫So when we pass this a value, instead of getting a singly linked list node, we're getting a doubly

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‫linked list node which has two pointers.

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‫Then we'll set head to be equal to the new node like this, we'll do the same thing with tail and that

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‫will point tail at that new node.

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‫And because that doubly linked list has that one item in it, we'll set the length to be equal to one.

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‫So let's bring back the rest of our code.

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‫That's the entire doubly linked list class so far.

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‫And I'll focus back in on the constructor like this.

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‫We'll run this constructor and create a new, doubly linked list with something like this.

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‫We're calling our new doubly linked list my doubly linked list and passing it a number seven.

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‫And when we run this line of code, we're getting all of this.

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‫We're getting a doubly linked list node with a value of seven head and tail are pointing at that node

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‫and the length is equal to one.

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‫So now let's flip over to this code and take a look at this.

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‫So there is our node class there for our doubly linked list and I'll scroll up here.

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‫And this is all of the code that we just wrote for our doubly linked list with the three member variables

44
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‫up here at the top and then the constructor down here.

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‫And just like I did with single link lists I created for member functions called Print List, get head,

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‫get tail and get length.

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‫These all work exactly the same way as they did in a singly linked list.

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‫And I'll scroll up again and we have our main function and this is the line of code that we just looked

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‫at that creates a new doubly linked list called My Linked List, and it will be initialized with one

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‫node with a value of seven.

51
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‫And then with this line here, we'll print out that linked list with that one item in it.

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‫So I'll run this.

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‫And you can see here we have a linked list with one node with a value of seven.

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‫And that is our doubly linked list constructor.