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Welcome back, everyone.

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So when you come up with your test case for these interface design questions, what will happen is that

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you're going to be expected to call your interface and its methods in a sequence of ways that built

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out the tree that I showed you in the previous example.

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Generally speaking, your interviewer may or may not walk through the problem as extensively as I did.

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But as you start thinking about test cases or conversing with your interviewer, a general picture of

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what we went through should emerge here.

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What you'll see will happen is that with our general test case, what we've done is initialized the

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monarchy with Jake as the king.

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So what we're doing is calling the methods in the same order that we went through in order to build

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out such a tree.

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So we need to call the birth of Katherine to Jake.

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And here you might change up the order in which these different calls happen, but it should not deviate

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from how this tree looks.

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In the end, the only thing to consider is the order in which children get born to their parent.

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What this means is that because Seline is the third child of Jake, you cannot call the birth of Seline

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before you call the birth of Tom, because if you do, then Saleen gets born before Tom does.

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This might be one of those cases where, as you're thinking about this test case, that's something

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that pops to your mind about the way that the children are ordered, because the succession of this

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example does matter by birth order.

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So that's an important thing you need to notice.

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So let's say, for example, Arthur Katherine gets born to Jake, Jane gets born to Katherine, then

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let's say father gets born to Jane and then Tom gets born to Jake here.

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It doesn't matter when Tom is born, as long as it's after Katherine.

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Katherine can have all of her children and you can call all of these arguments.

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However, you must call Tom before sailin.

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That's the real only order that matters as far as the children birth order goes.

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Let's say afterwards.

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Then Celine gets born to Jake and let's say Marc then gets born to Katherine and then Peter gets born

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to Celine.

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Even in this order, this is still the resulting tree for our best case test case example.

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So when you think about how you're designing the order of the calls of this monarchy, because at this

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point we know what these methods will do, we have to think about how it constrains to the give an example

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of what exactly we're trying to build is.

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And here this should be very clearly defined to you by your interviewer.

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When they told you about the monarchy family tree.

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You might want to discuss this as well as your writing this out, because at this point, when you're

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figuring out these methods and when to call them to form this tree, these might be the types of examples

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that are jumped to your head.

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So moving on from here, let's say we call, then get order of succession.

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Clearly, the order of succession goes Jake, then Catherine and then Jane and then Fera, because these

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are all of the first borns, first born children and subsequent first born children.

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And then after that, it goes Mark for Katherine and then it goes Tom and then finally Saleen and Peter.

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So this is the same order of succession we saw earlier.

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Let's say once again, we kill off Jake and we kill off Jane.

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What then happens if we scratch out these names?

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To represent their deaths, as that will see the new order of succession goes Katherine and then Farah,

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as you can see, and then it's Mark and then Tom and then Celine and Peter, which is also what you

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see in the remainder of the array.

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So this is going to be the order of calls that will come from the interface that we're expected to design

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as our test case.

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So with interface design questions, oftentimes what's going to happen is that they want to test that.

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The order of your sequencing of what the logic is intended to achieve with your interface is valid once

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you've designed the interface.

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So these are the different ways that you want to think about what kind of constraints you need to capture

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in the logic of the interface that you're designing.

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So now that we understand what it is that we're building here, I want you to try and see if you can

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figure out some of the insights so that you can try and solve this question yourself.

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Some hints that might help you before you dive in.

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You can pause the video here and try and figure out yourself or you can listen to me talk and then try

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it yourself, because in the next video, we're going to solve it all together.

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But what I want you to notice is that this is indeed a tree structure and the order of succession is

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probably the most challenging part here.

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What I want you to think about is the order in which these elements appear.

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And when you think about this tree, it's not a binary tree, but it is a binary tree, meaning that

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there are still these different tree nodes, but they might have any number of branches.

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So here you can still utilize the exact same traversal order, breadth versus depth research that we

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know with trees, because as we know with enteric trees, these are still trees at the end of the day,

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which means that our breadth of research and our depth research and even our subsequent order of the

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traversal, whether it's preorder in order or post order, these are all things that can help you.

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So I want you to think about this question in the context of what it's like to build out an energy tree

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and then perform one of these search algorithms.

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And when you do think about that order traversal, if it even helps you, so it's kind of a tree problem

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that's wrapped up inside of this interface.

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But this is where I mentioned that these different data structures that you already know could help

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you solve these problems.

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In fact, these problems are probably grounded in these data structures that you already know.

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So here, I want you to try and solve this question yourself.

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Think about that interface design, those three methods, birth, death and the order of succession

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and how it all ties together.

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I'm going to solve it with a JavaScript class in the next video.

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You might have to do it in your own native language implementation, whichever language you choose to

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do.

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And in the next video, let's do it together.