25. Trie
Prefix trees for words, autocomplete and XOR tricks.
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Understand the topic
A trie (prefix tree) stores words letter by letter. Words that share a beginning share a path, so "car", "cart" and "care" all use the c → a → r nodes. Each node has up to 26 children and a flag that says "a word ends here".
Lookups take O(word length), however many words are stored. Tries power autocomplete and prefix search. A binary trie (two children per node, one per bit) also solves maximum-XOR problems.
| # | Problem | Pattern | Level | ||
|---|---|---|---|---|---|
| 1 | Implement Trie (Prefix Tree) #208 | Trie basics | Medium | LeetCode ↗ | |
| 2 | Design Add and Search Words Data Structure #211 | Trie + DFS for wildcards | Medium | LeetCode ↗ | |
| 3 | Search Suggestions System #1268 | Trie with top-3 lists | Medium | LeetCode ↗ | |
| 4 | Replace Words #648 | Shortest root in a trie | Medium | LeetCode ↗ | |
| 5 | Longest Word in Dictionary #720 | Trie walk through complete words | Medium | LeetCode ↗ | |
| 6 | Maximum XOR of Two Numbers in an Array #421 | Binary trie | Medium | LeetCode ↗ | |
| 7 | Word Search II #212 | Trie-guided grid DFS | Hard | LeetCode ↗ | |
| 8 | Maximum XOR With an Element From Array #1707 | Offline queries + binary trie | Hard | LeetCode ↗ |
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Work top to bottom — each list goes from easy to hard. Try a problem for at least 15 minutes before opening a hint. Ticks are saved in your browser.