[?*]Letter Combinations of a Phone Number

 1   public class Solution {
 2         public static List<String> letterCombinations(String digits) {
 3             String digitletter[] = {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
 4             List<String> result = new ArrayList<String>();
 5 
 6             if (digits.length()==0) return result;
 7 
 8             result.add("");
 9             for (int i=0; i<digits.length(); i++) 
10                 result = combine(digitletter[digits.charAt(i)-‘0‘],result);
11 
12             return result;
13         }
14 
15         public static List<String> combine(String digit, List<String> list) {
16             List<String> result = new ArrayList<String>();
17 
18             for (int i=0; i<digit.length(); i++) 
19                 for (String x : list) 
20                     result.add(x+digit.charAt(i));
21 
22             return result;
23         }
24     }