1804. Implement Trie II (solutions/Prefix Tree)

https://leetcode.com/problems/implement-trie-ii-prefix-tree

Description

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.

• int countWordsEqualTo(String word) Returns the number of instances of the string word in the trie.

• int countWordsStartingWith(String prefix) Returns the number of strings in the trie that have the string prefix as a prefix.

• void erase(String word) Erases the string word from the trie.

Example 1:

**Input**
["Trie", "insert", "insert", "countWordsEqualTo", "countWordsStartingWith", "erase", "countWordsEqualTo", "countWordsStartingWith", "erase", "countWordsStartingWith"]
[[], ["apple"], ["apple"], ["apple"], ["app"], ["apple"], ["apple"], ["app"], ["apple"], ["app"]]
**Output**
[null, null, null, 2, 2, null, 1, 1, null, 0]
**Explanation**
Trie trie = new Trie();
trie.insert("apple");               // Inserts "apple".
trie.insert("apple");               // Inserts another "apple".
trie.countWordsEqualTo("apple");    // There are two instances of "apple" so return 2.
trie.countWordsStartingWith("app"); // "app" is a prefix of "apple" so return 2.
trie.erase("apple");                // Erases one "apple".
trie.countWordsEqualTo("apple");    // Now there is only one instance of "apple" so return 1.
trie.countWordsStartingWith("app"); // return 1
trie.erase("apple");                // Erases "apple". Now the trie is empty.
trie.countWordsStartingWith("app"); // return 0

Constraints:

• 1 <= word.length, prefix.length <= 2000

• word and prefix consist only of lowercase English letters.

• At most 3 * 104 calls in total will be made to insert, countWordsEqualTo, countWordsStartingWith, and erase.

• It is guaranteed that for any function call to erase, the string word will exist in the trie.

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