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LC 79 Word Search and LC 212 Word Search II ship in nearly every FAANG onsite. Master DFS with in-place visited marking, four-directional exploration, and the trie trick that turns multi-word search into a single traversal.
Word Search II (LC 212) is the canonical FAANG hard combining trie data structures with grid backtracking. Build a trie from the dictionary, DFS each cell, and prune aggressively to convert an exponential brute force into a fast practical algorithm.
Master Tries for FAANG interviews: insert, search, prefix operations, Word Search II, autocomplete, XOR binary trie for max XOR, and 5-language implementations with full problem index.