Tries
Prefix trees for efficient string operations — search, autocomplete, and XOR tricks
0/32 solved
Insert / Search / StartsWith
Core trie operations for prefix-based string lookups
Approach
Build a tree where each node represents a character. To insert, traverse/create nodes character by character. To search, traverse nodes — return true only if the last node has isEnd=true. StartsWith is the same but doesn't check isEnd.
How to Recognize
Need efficient prefix matching across many strings
Problem involves autocomplete or dictionary lookup
Phrases like 'implement trie', 'prefix search', 'magic dictionary'
Multiple string queries on a fixed dictionary
Pro Tips
Each node has up to 26 children (for lowercase English) and an isEnd flag
Use HashMap children for large alphabets or Unicode
Trie search is O(L) where L is word length, regardless of dictionary size
8
Total
1
Easy
6
Medium
1
Hard
Time
O(L) per operation where L = word length
Space
O(N * L) for N words