I knew the concept but fumbled the implementation a bit.
Start by clarifying the requirements and constraints, then design a Trie node with children (e.g., array or hashmap) and an isEndOfWord flag. Implement insert, search, and startsWith methods, and analyze time and space complexity. Consider edge cases like empty strings and large alphabets.
Pro tip: Mention that using a hashmap for children can save space for sparse tries, but an array of size 26 is faster for dense lowercase English alphabets. Also, discuss how to handle deletion if asked, and note that Trie is ideal for autocomplete and spell-check.
Ask about the character set (e.g., lowercase English letters), maximum word length, and whether deletion is needed. Confirm the expected time and space complexity.
Define a TrieNode class with a children data structure (array or hashmap) and a boolean flag isEndOfWord. Explain your choice based on the character set and memory considerations.
For insert, traverse or create nodes for each character and mark the last node as end of word. For search, traverse and return true only if the last node is marked as end. For startsWith, traverse and return true if the prefix exists, regardless of end flag.
State that time complexity for all operations is O(L) where L is the word length, and space is O(N*L) for N words. Discuss edge cases: empty string, very long words, and non-alphabetic characters.
Walk through a small example like inserting 'apple' and searching 'app'. Mention possible optimizations like using a ternary search tree or compressed trie (radix tree) for memory efficiency.
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