DSA · Theory

Hash Table

Theory

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Hash Table is a DSA topic. In plain words you use it for name → phone in a diary. Don’t start with a slogan — start with that picture.

Smallest example: key % size + collision plan. Type it, run it, and say what you see. If you can do that from memory, you know Hash Table.

From the example next to this theory — Hash Table — hash maps give average O(1) insert/lookup — dict in Python.

Trap — bad hash → pile-up. Fix that before you talk about advanced DSA.

Viva — what is Hash Table? Then show key % size + collision plan. Then name the trap.

Exam tip

What is Hash Table? Show this: key % size + collision plan. Trap: 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 Table — hash maps give average O(1) insert/lookup — dict in Python.