Kahn's algorithm (BFS) sketch for topological ordering of DAGs.
Short memoization template and when to convert recursion → DP.
Short notes on idempotent vs non-idempotent operations and retry semantics.
Compact cheat-sheet for tries: insertion, search, and common uses (autocomplete).
When to use BFS vs DFS and a tiny BFS snippet for shortest unweighted paths.
Binary search templates and edge-case patterns (lower_bound, upper_bound).
