#17
Letter Combinations of a Phone Number
medium · verified · 65.6% accepted · 20,830 likes · top 70%
hash table · string · backtracking
Description
Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
Example 1:
Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
Example 2:
Input: digits = "2"
Output: ["a","b","c"]
Solution