Hash Map Insert/Lookup Complexity (Big-O)

A hash map supports expected O(1) insert, lookup, and delete via a hash function; the worst case is O(n) when many keys collide. Space is O(n).

Key facts

Frequently asked questions

What is the time complexity of hash map insert?

O(1) expected, O(n) worst case under heavy collisions.

Why is hash map worst case O(n)?

When many keys hash to the same bucket, operations degrade to a linear scan.

Related pages

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