Hash maps

New idea

Finding Sara without searching

You have 1,000,000 contacts and want Sara's number. Linear search could check a million names. Binary search needs about 20 guesses, and only after sorting. A hash map usually needs about 1 step. No sorting at all.

A hash map stores key → value pairs: a name and its phone number, or a word and its meaning. You hand it the key and it gives back the value.

Python dictionaries and JavaScript objects work like this. In code, ages = {"Sara": 12} stores the key "Sara" with the value 12, and ages["Sara"] reads it back.