↓Skip to main content

Iterator

LeetCode 173: Binary Search Tree Iterator

2026-10-24·2 mins

LeetCode Medium Stack Tree Design Binary-Search-Tree Binary-Tree Iterator

LeetCode 173 note: flattening to an array is simple but uses O(n) space; the follow-up keeps the left spine on a stack for amortized O(1) and O(h) space

Queue and Design Problems

2026-10-20·3 mins

Algorithm Queue Design Iterator Lazy-Deletion

Circular queues, zigzag iterators, FIFO matching with cancellation, and the data structure combinations that design problems keep using

LeetCode 281: Zigzag Iterator

2026-04-29·2 mins

LeetCode Medium Queue Design Iterator

LeetCode 281 note: a queue of unfinished sources, take one value in turn and put the source back if anything remains; it generalizes to k sources