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Leaves - Morgan #21

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Heaps Practice

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Comprehension Questions

Question Answer
How is a Heap different from a Binary Search Tree? Heap guarantees that elements on higher levels are greater or smaller (depending on max or min heap) than elements on lower levels.
Could you build a heap with linked nodes? Yes, but mostly done with arrays.
Why is adding a node to a heap an O(log n) operation? We need at most one swap on each level of a heap on the path from the inserted node to the root.
Were the heap_up & heap_down methods useful? Why? Yes, these maintain the order of the heap.

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@CheezItMan CheezItMan left a comment

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Really nice work, some small issues with time/space complexity, but you hit the main learning goals here. Well done!

Comment on lines +4 to 6
# Time Complexity: I think this is O(n)? It touches every item in the list
# Space Complexity: O(n)? - creating new sorted array
def heap_sort(list)

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For time complexity it does touch every item, but removing and adding an item to a heap is O(log n), so this algorithm is O(n log n). Otherwise well done.

Comment on lines +17 to 20
# Time Complexity: I think O(log N)
# Space Complexity: O(1) - I think this is for all space regardless of operation because it's not necessarily
#growing all that much in size?
def add(key, value = key)

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Since heap_up is recursive you need to account for the system stack in the space complexity. So Space complexity is O(log n). Otherwise well done.

def empty?
raise NotImplementedError, "Method not implemented yet..."
return true if @store.empty?

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Suggested change
return true if @store.empty?
return @store.empty?

Comment on lines +59 to 61
# Time complexity: O(1)
# Space complexity: O(1)
def empty?

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👍

Comment on lines +70 to 72
# Time complexity: O(log n)
# Space complexity: O(1)
def heap_up(index)

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See above regarding space complexity (add).

end


# This helper method takes an index and
# moves it up the heap if it's smaller
# than it's parent node.
def heap_down(index)

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👍 Well done!

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2 participants