Phone Number Combinations

Given a string of digits representing a phone number, return all possible letter combinations that can be formed based on the mapping on a standard phone keypad. Implement a Trie to manage the combinations. Input Format: The input is a string of digits, where each digit is between '2' and '9'. The length of the string will be between 1 and 10 digits long. Output Format: Print all possible combinations that can be formed, one per line in lexicographical order. Example: Input: 23 Output: ad ae af bd be bf cd ce cf