DSA · Theory

Hash Functions

Theory

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If you can teach Hash Functions using name → phone, you know it. If you only know the heading, you don’t.

For Hash Functions, time vs memory is in play. Don’t blame it until you have traced name → phone.

Skip Hash Functions and bad hash → pile-up shows up in a diary.

Isha ships Hash Functions in a diary. That is the use case worth saying.

Don’t do this with Hash Functions — bad hash → pile-up. Interviewers spot it in ten seconds.

Hash Functions is not a lonely heading. Isha ties it to name → phone.

Viva for Hash Functions — what it is → key % size + collision plan → the mistake (bad hash → pile-up).

Exam tip

Say Hash Functions in one breath, then key % size + collision plan, then bad hash → pile-up.

freq = {}
for ch in "banana":
    freq[ch] = freq.get(ch, 0) + 1
print(freq)
print(freq.get("a"), freq.get("z", 0))

Hash Functions — hash maps give average O(1) insert/lookup — dict in Python.