Key-value pairs for lookup

Day 136 of 149

👉 Full deep-dive with code examples

The Phone Book Analogy

Remember phone books?

Find "Smith" → Flip directly to S section

Look up the name → Get the phone number

You don't scan from the beginning!

Maps work like phone books!

You look up a "key" (name) and instantly get a "value" (phone number).

The Problem They Solve

Looking up things in a list is slow:

1 million items?

Check one by one?

That could take forever!

With a map:

Store key → value pairs

Look up by key

Get the answer instantly!

How Maps Work

Maps store pairs of things:

Key → Value "name" → "Alice" "age" → 30 "city" → "Sydney"

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To get a value, just use the key:

Ask for "name" → Get "Alice"

Ask for "age" → Get 30

No searching through everything!

Why They're Fast

Behind the scenes, maps use a smart trick:

Convert the key to a number (hashing)

Use that number to find the exact location

Go directly there

Like a library catalog card…