Algorithms

An LRU cache is a perfect little systems problem: a dictionary for O(1) lookup plus a linked list for recency. Let's build one in Swift, test it, and talk about when OrderedDictionary is the simpler app-level choice.

Binary search is less scary when you commit to one invariant. Let's implement lowerBound, upperBound, exact search, and insertion index in Swift using half-open ranges and test cases that catch the usual mistakes.

The sliding window maximum problem is a great example of why the right data structure matters. Let's solve it in Swift with a monotonic deque and get the runtime down to O(n)...

Solve LeetCode problem 21 in Swift by merging two sorted linked lists iteratively and recursively, with the tradeoffs of each approach.

Solve longest substring without repeating characters in Swift using a sliding window and a dictionary of character indexes.