FAQ: Heaps: Python - Translating Parent and Child Elements Into Indices

This community-built FAQ covers the “Translating Parent and Child Elements Into Indices” exercise from the lesson “Heaps: Python”.

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This exercise can be found in the following Codecademy content:

Computer Science

Complex Data Structures

FAQs on the exercise Translating Parent and Child Elements Into Indices

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How would we a represent a heap that, somewhere in the middle of it, a node only has one child but that child has two children itself? For example, if we had the following heap:
…3…4 |… 5…
…|…6… 7
How would we represent it as a list? I tried but I got the following [0, 1, 2, 3, 4, 5, ?, 6, 7]
What goes in the ‘?’
This also makes it tough to use the parent, left_child, and right_child methods. Please help.

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Unlike a tree, a heap is not defined by designated parent-child relationships, but is purposely constructed top-to-bottom, and left-to-right, so that the indexing scheme holds and the remove or add algorithm maintains the min or max structure of the heap.

In other words, as far as I can see, the situation you describe would never arise with a heap. After 0, 1, 2, 3, 4, and 5 were added to your heap, 6 would be forced to occupy the position next to 5 as the rightmost child of 2, and 7 would be the leftmost child of 3.


Could anyone explain to me why the parent index of index 4 is 2?

This is only the case when your root index is 1. When the root index is 0, the parent of index 4 is 1:

1 2
3 4 5 6

And according to the exercise they are using root index 0:

[None, 10, 13, 21, 61, 22, 23, 99]
Indices: [0, 1, 2, 3, 4, 5, 6, 7]

Yet with the arithmetic for a root index 1 heap:

  • Parent: index // 2
  • Left Child: index * 2
  • Right Child: (index * 2) + 1

Or am I missing something? Am I completely off base here?!?

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I am wondering the same thing. Can anyone shed light on this please?

1 Like

The tree is actually
2 3
4 5 6

The first index is None and should actually be ignored. In other websites it seems conventional to not even have None in the index. The root is at index 1 with the value 10.

So yes, you were literally “off base” lol.