Leaves-Yasmin

[YasminM11]

Hash Table Practice

Congratulations! You're submitting your assignment!

Comprehension Questions

Question	Answer
Why is a good Hash Function Important?	To provide a time complexity of O(1) for insert, delete and search
How can you judge if a hash function is good or not?	A good hash function has the following attributes: - Fast computation of the hash value - Hash values are uniformly distributed - Keys that are close have hash values that are far apart
Is there a perfect hash function? If so what is it?	Yes, A hash function for which there are no collisions is called a "perfect hash function"
Describe a strategy to handle collisions in a hash table	Separate Chaining: uses a linked list to store the collided keys
Describe a situation where a hash table wouldn't be as useful as a binary search tree	Hash tables are not good for finding ordered data. Linked list and binary search tree can get us the min and max in O(n) and O(log n) time.
What is one thing that is more clear to you on hash tables now	I learned the ways to handle collisions in a hash table. Need more practice

[CheezItMan]

The first works well. The second happens to pass the tests, but doesn't actually work in general. Take a look at my comments and let me know if you have questions.

[CheezItMan]

Except for any general purpose hash, no hash function can be perfect.

[CheezItMan]

👍 Nice

[CheezItMan]

I believe hash.sort sorts elements by the key instead of the value, so this will return the elements sorted by the keys instead of the frequency of their occurrence in the original array.

It's happening to pass the tests, but it's not working in general.

Consider this:

    it "will work for [3, 3, 3, 3, 3, 1, 1, 2, 2, 2]" do
      list = [3, 3, 3, 3, 3, 1, 1, 2, 2]
      k = 2

      answer = top_k_frequent_elements(list, k)

      expect(answer.sort).must_equal [2, 3]
    end

Also even if this did work, you're sorting the hash each iteration of the loop... which is excessive.

[CheezItMan]

This doesn't actually work (see below) and is O(k * n log n) in time complexity as you're sorting the hash k times.