Implement Trie (Prefix Tree)

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.   **Example 1:** **Input** ["Trie", "insert", "search", "search", "startsWith", "insert", "search"] [[], ["apple"], ["apple"], ["app"], ["app"], ["app"], ["app"]] **Output** [null, null, true, false, true, null, true] **Explanation** Trie trie = new Trie(); trie.insert("apple"); trie.search("apple"); // return True trie.search("app"); // return False trie.startsWith("app"); // return True trie.insert("app"); trie.search("app"); // return True ```   **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`, `search`, and `startsWith`.