01 — problem
Contains Duplicate II — LeetCode #?. Full problem statement, examples, and constraints live at https://leetcode.com/problems/contains-duplicate-ii. PatternLens tracks this problem for pattern coverage and progress tracking.
02 — notes
Full examples and constraints live on the original LeetCode prompt. Use the link in the sidebar when you want the canonical statement.
03 — hints
Start by identifying the core hash tables idea that reduces the search space.
If you get stuck, check whether a standard hash tables technique applies here.