17. Letter Combinations of a Phone Number(bfs)

Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.

Example:

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

Note:

Although the above answer is in lexicographical order, your answer could be in any order you want.

 1 class Solution {
 2     public List<String> letterCombinations(String digits) {
 3         LinkedList<String> res = new LinkedList<String>();
 4         if(digits.isEmpty()) return res;
 5         String[] mapping = new String[] {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
 6         res.add("");
 7         for(int i=0;i<digits.length();i++){
 8             int x=Character.getNumericValue(digits.charAt(i));
 9             while(res.peek().length()==i){
10                 String t = res.remove();
11                 for (char s :mapping[x].toCharArray())
12                     res.add(t+s);
13             }
14         }
15         return res;
16     }
17 }

原文地址：https://www.cnblogs.com/zle1992/p/9313868.html