一、问题详情:
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。答案可以按 任意顺序 返回。给出数字到字母的映射如下(与电话按键相同)。注意 1 不对应任何字母。
示例 1:
输入:digits = "23" 输出:["ad","ae","af","bd","be","bf","cd","ce","cf"]
示例 2:
输入:digits = "" 输出:[]
示例 3:
输入:digits = "2" 输出:["a","b","c"]
提示:
0 <= digits.length <= 4