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LeetCode 208, Medium. Topics: Hash Table, String, Design, Trie. View on LeetCode. Generate this problem as a practice environment: tested reference solution, 12 parametrized pytest cases, and a playground notebook:

Problem

A trie (pronounced as “try”) or prefix tree is a tree data structure used to efficiently store and retrieve keys in a dataset of strings. There are various applications of this data structure, such as autocomplete and spellchecker. Implement the Trie class:
  • Trie() Initializes the trie object.
  • void insert(String word) Inserts the string word into the trie.
  • boolean search(String word) Returns true if the string word is in the trie (i.e., was inserted before), and false otherwise.
  • boolean startsWith(String prefix) Returns true if there is a previously inserted string word that has the prefix prefix, and false otherwise.

Examples

Explanation:

Constraints

  • 1 <= word.length, prefix.length <= 2000
  • word and prefix consist only of lowercase English letters.
  • At most 3 * 10^4 calls in total will be made to insert, search, and starts_with.

Solution

Reference implementation from solution.py on GitHub, full suite in test_solution.py:

Complexity

Tags

Grind 75, Grind, Blind 75, NeetCode 150, NeetCode 250, NeetCode All, AlgoMaster 75.
Last modified on August 25, 2026