Core · Module 7 · Lesson 4 of 11

Associative Containers: map, set and unordered_map

Pick ordered versus hashed lookup for the catalogue, compare O(log n) tree cost against average O(1) hashing, and use map, set and unordered_map without surprises.

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By the end you can

Compare ordered tree and hash table guarantees for lookup and iteration
Use map, set and unordered_map for catalogue id and title search
Predict invalidation, hash cost and ordering effects on performance

Builds on string: Characters, Storage and Small-String Optimization.

01 · A question first

You need title lookup by id and by keyword, plus a duplicate check for ISBN codes. One container keeps everything sorted, another answers in constant time but scrambles order. Which one holds the catalogue index, what does each lookup really cost, and when does hashing lose?

Make a guess before you read on.

02 · The idea

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What's inside

Start with the problem
How the idea works
Why it is correct
What it costs
Pitfalls and variations
How to choose the index for a query
Where it is used