The core structure wasn't the hard part, it's making sure your node traversal doesn't do anything dumb at scale.
Start by clarifying the requirements and constraints, then propose a Trie with an array of 26 child pointers per node and a boolean end-of-word flag. Explain the O(L) time complexity for each operation and discuss memory optimizations given the large input size. Finally, walk through the implementation and test with edge cases.
Pro tip: Mention that using a fixed-size array for children is faster but memory-heavy; for 2M characters, consider a hash map or compressed trie to reduce memory. Also, discuss how to handle large inputs with iterative approaches to avoid stack overflow.
Ask about character set (lowercase English?), input size limits, and whether memory or speed is more critical. Confirm that operations are insert, search, and startsWith.
Define a TrieNode with children (array of size 26 or hash map) and a boolean isEnd. Explain how each operation traverses the tree character by character.
State that time complexity is O(L) per operation, where L is word length. Discuss space complexity O(N*L) and compare array vs hash map for children.
Write clean code for insert, search, and startsWith, handling null/empty strings and ensuring proper node creation. Use iterative loops to avoid recursion depth issues.
Walk through examples, test edge cases (empty string, single character, long words), and mention potential optimizations like compressed trie or memory pooling.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.