- 1
Letters as Edges
A trie stores strings one character-edge at a time: shared prefixes share a path, and a word-end flag marks where real words stop.
Complete codeMultiple choiceTap - 2
Longest Common Prefix
Scan column by column across all strings at once, and stop at the first disagreement — or when the shortest string runs out.
Complete codeMultiple choiceTrace - 3
Implement Trie (Prefix Tree)
Build the canonical node — children[26] plus an isWord flag — and see why search and startsWith differ by exactly one check.
Complete codeDebugCode orderMultiple choiceTrace - 4
Replace Words
Insert every root into a trie, then walk each sentence word and stop at the FIRST word-end — the shortest root wins automatically.
Complete codeDebugMultiple choiceTrace - 5
Longest Word in Dictionary
A word qualifies only if EVERY prefix of it is also a word — so DFS the trie and refuse to step onto any node that isn't a word-end.
Complete codeDebugMultiple choiceTrace - 6
Search Suggestions System
Autocomplete = one trie cursor that advances a single edge per keystroke, plus a DFS that collects the 3 smallest words below it — sorted order comes from the alphabet, not from sorting.
Complete codeDebugMultiple choiceTrace - 7
Tries CheckpointCheckpoint
No new concepts — carry the island's trie moves into unseen problems: counting contacts by prefix, summing values under a prefix, camelCase matching, and prefix-free code checks.
Complete codeCode orderMultiple choiceTrace - 8
Tries ReviewReview
Mixed recap of the island: node anatomy and the isWord flag, insert vs search asymmetry, when a trie beats a hashset, shortest vs longest root walks, enumerating below a node, and what bounds a trie's size.
Complete codeCode orderMultiple choice - 9
Boss: Add and Search WordsBoss
The island's final test: a word dictionary whose search allows '.' wildcards. A hashset cannot hash a wildcard, and a trie walk cannot pick just one child — at every '.', DFS must fan out across ALL children, and one success anywhere wins.
Complete codeDebugCode orderMultiple choiceTrace
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