Module 3 · 5 lessons · about 260 minutes
Arrays and hash maps
How a list sits in memory, how a hash map finds a key without searching, and the patterns they power: counting, seen-before, grouping by a key, and prefix sums.
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- Exercises
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- Code
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- Checkpoint
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- 1How a list really works40 min
- 2How a hash map works50 min
- 3Counting and seen-before60 min
- 4Grouping by a key55 min
- 5Prefix sums55 min
Problems for this module
The lessons teach some of these step by step (each says which). The rest are practice: try each in its target time, and solved problems come back for spaced re-solves.