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LC 78 is the gateway to every combination and permutation problem in FAANG interviews. Master all three approaches — backtracking, bitmask enumeration, and iterative cascading — with deep visual dry runs, real interview follow-ups, and line-by-line Python and JavaScript solutions.
Master LeetCode 209 from first principles: understand why a variable-size shrinkable sliding window is the insight that cracks this problem in O(n), trace through every pointer movement on a real example, learn the three common interview mistakes, and be ready for the O(n log n) binary search follow-up that Amazon and Microsoft love to ask.
LeetCode 442 is a FAANG favorite that tests whether you can squeeze O(1) space out of a hash-set problem. We use index negation to mark visited values in place.
LeetCode 394 is a classic FAANG string problem testing nested-bracket parsing. We use two stacks to decode any depth of k[encoded] expressions in linear time.
LeetCode 40 is a FAANG backtracking favorite that tests duplicate handling. Sort the candidates and skip same-level repeats to enumerate unique sum combinations.