Kahn's algorithm (BFS) sketch for topological ordering of DAGs.
Short memoization template and when to convert recursion → DP.
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).
Pattern notes: when to use fixed-size vs variable-size sliding windows.
Find pair summing to target using a hashmap; common interview pattern.
Compact reference for merge sort: idea, complexity and a short implementation.
