Combinations

2 articles

dsa10 min read

Combinations and Combination Sum — The Start-Index Backtracking Pattern

LC 77 Combinations, LC 39 Combination Sum, and LC 40 Combination Sum II form a trilogy that every FAANG interviewer loves. Master the start-index pattern to enumerate selections without duplicates and the i+1 vs i reuse trick.

March 19, 2026Read →

dsa8 min read

Letter Combinations of a Phone Number — Cartesian Product Backtracking

LC 17 Letter Combinations of a Phone Number is the cleanest cartesian-product backtracking template ever written. Master the digit-to-letter mapping, the per-position branching, and why the iterative BFS variant is asked at Amazon.

March 19, 2026Read →