title: "Lecture notes — 2026-04-07 (abstract data types)" project: "cs101-intro" tags:

• lecture
• study-notes
• cs101 date: 2026-04-07

Lecture 2026-04-07 — Abstract data types

Source — Live lecture + import from audio transcription (Otter.ai export, cleaned 2026-04-07 evening).

Summary (5 bullets)

• ADT = behavior contract separate from implementation.
• List ADT can be array-backed or linked; tradeoffs: cache locality vs. insert cost.
• Iterator pattern hides internal structure from client code.
• Big-O today focused on worst case unless stated otherwise.
• Prof emphasized: choose the ADT first, then pick the implementation.

Detailed notes

• Array list — doubling strategy keeps append amortized O(1); wasted space bounded by a constant factor.
• Singly linked list — O(1) insert at head; need tail pointer for O(1) enqueue in naive queue.
• Invariant example: size field must equal length walked from head.

Questions for office hours

• Why not use Python list for everything in homework if industry does?
  Answer (from slide footer) — Pedagogy: you implement to see why the optimizations exist.

Homework link

Maps directly to assignments/week-3-data-structures.md — start Stack tonight.