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‫So now we're going to create our add vertex function and add vertex is just going to create one of these

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‫and the next video will learn how to add edges and then we can create a graph like this.

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‫But for now, we're just creating this.

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‫And when we create that, it's going to look like this.

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‫So I'm going to move this down to the bottom and we need to start writing our class, which is called

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‫graph.

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‫And before we actually get into the add vertex function, we need to create that unordered map that

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‫will store our graph.

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‫N And then once we have that created, we can create vertices like this.

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‫So that unordered map will be created with this line.

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‫So this is an unordered map where the key is a string.

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‫That's the A in this case, and then the value is an unordered set of strings.

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‫So this would be the value in this key value pair.

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‫And then we will call this unordered map adjacency list.

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‫So this line of code is going to give us an empty unordered map, and then we need to write the function

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‫to put this into the unordered map.

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‫So for now, I'm going to remove this and now we'll start writing the function to add the vertex.

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‫So let's focus in just on this code.

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‫In order to add an item to this unordered map, we can just do this and say into the adjacency list,

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‫we're going to pass this vertex and that does this.

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‫So one of the things I want to point out here is if you change this Boolean to a void.

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‫This is a complete function just like this.

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‫But I'm going to write my function a little bit differently.

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‫What I'm going to do is check to see is that vertex already in the adjacency list and I'm going to do

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‫that with this code.

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‫So we're going to say if adjacency list count for that vertex equals zero.

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‫In other words, this vertex is not already in the adjacency list.

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‫If that is the case, only then are we going to run this line.

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‫And then after we do this, we'll return true, true that we were able to add a vertex.

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‫And then if the conditional in the if statement is false, we'll skip the if statement and return false.

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‫And like I said, all of this is not necessary.

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‫We could change this to void and just run this one line.

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‫But doing it this way where it returns true or false, gives us a little bit more visibility into what's

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‫going on.

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‫So that is all of our code for ADD Vertex.

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‫Now let's flip over to VS Code and take a look at this.

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‫So to start off with, we'll need these two lines because we're using an unordered map and an unordered

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‫set.

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‫And I'm going to scroll up a little bit here.

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‫And this is the code here that creates that unordered map.

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‫And then I created a function called print graph so we could print this out.

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‫And this is the add vertex function that we just created.

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‫And I'll scroll up again.

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‫And in our main function this creates our new graph and with this line we're adding that new vertex

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‫with a value of a and with this line we'll run that print graph function and I'll run this.

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‫And you can see up here that we've been able to add that vertex with the value of A and it has an empty

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‫unordered set and that is our function for ADD Vertex.