Earth - Anya

[anyatokar]

Hash Table Practice

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Comprehension Questions

Question	Answer
Why is a good Hash Function Important?	A good hash function is important for a well-functioning and efficient hash map.
How can you judge if a hash function is good or not?	1. It's consistent (h(key) always results in same number). 2. Maps different keys to different values (for the most part). 3. Executes in constant time (efficient). 4. Should appear to be random (but reversible in hash tables).
Is there a perfect hash function? If so what is it?	No, there isn't. Looking for a function that is easy to compute, maps input correctly, and minimizes collisions.
Describe a strategy to handle collisions in a hash table	One strategy is chaining, where each element of the hash table's internal array is a head of a linked list.
Describe a situation where a hash table wouldn't be as useful as a binary search tree	Keeping track of something in order by key.
What is one thing that is more clear to you on hash tables now	Learned what a hash function is.

[CheezItMan]

Nice work Anya, I had some feedback regarding space/time complexity. Hopefully my feedback here is clear. Let me know if it's not and I'm happy to try to clarify.

[CheezItMan]

👍 But the time complexity is O(n) if the strings are limited in size (so you can ignore the sort because it's limited in size), or O(n * m log m) where m is the length of the strings, if the string is not limited in size.

[CheezItMan]

👍 The time complexity is O(n log n) because you have an O(n) loop (the list.each loop) then a sort (O(n log n)), and followed by another loop which goes k times where k <= n.

So the time complexity is O(n + n log n + k) ==> O(n log n) because n log n is the dominate term. It's larger than n and k.

In the space complexity you're creating a hash O(n), a sorted hash O(n), and k_most_common_ele. So O(n + n + k) and so the final space complexity is O(n).