Q17 Letter Combinations of a Phone Number
Q17 Letter Combinations of a Phone Number

Given a digit string, return all possible letter combinations that the
number could represent.

A mapping of digit to letters (just like on the telephone buttons) is
given below.

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

robertzm/algotest