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Earth - Beauttie #14

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@beauttie beauttie commented Apr 22, 2021

Hash Table Practice

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Comprehension Questions

Question Answer
Why is a good Hash Function Important? To have fewer collisions and prevent the time complexity of lookup from approaching O(n)
How can you judge if a hash function is good or not? A good hash function is consistent (maps the same key to the same number), maps different keys to different values and distributes them uniformly across the array, executes in constant time, and difficult to reverse.
Is there a perfect hash function? If so what is it? It does not exist.
Describe a strategy to handle collisions in a hash table Quadratic probing searches for an empty bucket in the array that the hash table is built on by applying a function on each attempt of a search.
Describe a situation where a hash table wouldn't be as useful as a binary search tree When you need to maintain ordered data.
What is one thing that is more clear to you on hash tables now Examples of hash functions

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@CheezItMan CheezItMan left a comment

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Really nice work here Beauttie. You hit the learning goals here. Well done.

lib/exercises.rb Outdated
Comment on lines 4 to 7
# Time Complexity: O(n^2)
# Space Complexity: O(n)

def grouped_anagrams(strings)

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👍 Interesting solution with char.ord This works if you know that all the letters are a-z and roughly the same length. That's because you could end up with two strings of different lengths that have the same sum of characters.

Comment on lines +26 to 28
# Time Complexity: O(n)
# Space Complexity: O(n)
def top_k_frequent_elements(list, k)

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👍 I like the O(n) solution here.

return true
end

def valid_boxes(table)

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I like the helper methods here.

# Time Complexity: ?
# Space Complexity: ?
# Time Complexity: O(1) because the table has nine rows and columns
# Space Complexity: O(1) because each hash will store up to nine cells
def valid_sudoku(table)

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👍

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2 participants