17.letter Combinations of a Phone Number - 2018-07-26 00:17:05

题目 Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. 给定一个仅包含数字 2-9 的字符串,返回所有它能表示的字母组合。 A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. 给出数字到字母