小白笔记------------------------------------------leetcode（17. Letter Combinations of a Phone Number）

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”].

这道题用到了先入先出队列，这里还是mark一下

class Solution {
    public List letterCombinations(String digits) {
       LinkedList st = new LinkedList();
         if(digits.isEmpty()){
            return st;
        }
       String[] map = {"0","1","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
       String t = null;
       st.add("");

       for(int j = 0; j < digits.length();j++){
           int i = Character.getNumericValue(digits.charAt(j)); 
           while(st.peek().length() == j){
               t = st.remove();
               for(char ss : map[i].toCharArray()){
                   st.add(t+ss);
               }
           }
       }
        return st;
    }
}