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LeetCode 472 — find every word that can be formed by concatenating two or more shorter words from the same list. Trie accelerates the prefix-membership test inside a Word Break DP, turning O(2^L) brute force into O(N times L^2).
LeetCode 820 — encode a list of words into the shortest reference string where each word appears as a suffix terminated by #. Build a trie of reversed words; only words at trie leaves contribute their length plus one to the answer.
LeetCode 677 — design a structure supporting insert(key, value) and sum(prefix) returning the total of values for all keys with that prefix. The key trick is propagating delta sums along the trie path so prefix queries become a single O(L) walk.
LeetCode 2185 — count how many strings in words have pref as a prefix. The simple linear scan is optimal for a single query; the trie shines once you anticipate many queries against the same word list.
LeetCode 1707 — for each query (xi, mi), find max xi XOR nums[j] where nums[j] does not exceed mi. Sort queries by mi, sort nums, insert lazily into a binary trie, answer each query in O(32). The offline-trie pattern unlocks bounded XOR queries.