Letter Combinations of a Phone Number

Given a digit string, 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.

Input:Digit string "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 public class Solution {

 2     String[] c={    "",

 3                     "",

 4                     "abc",

 5                     "def",

 6                     "ghi",

 7                     "jkl",

 8                     "mno",

 9                     "pqrs",

10                     "tuv",

11                     "wxyz"  };

12     public List<String> letterCombinations(String digits) {

13         ArrayList<String> result = new ArrayList<String>();

14         search(digits, 0, new StringBuilder(), result);

15         return result;

16     }

17     

18     public void search(String dig, int index, StringBuilder sb, ArrayList<String> result){

19         if(index == dig.length()){

20             result.add(sb.toString());

21             return;

22         }

23         int num = dig.charAt(index) - '0';

24         for(int i = 0; i < c[num].length(); i ++){

25             StringBuilder sbs = new StringBuilder(sb);

26             sbs.append(c[num].charAt(i));

27             search(dig, index + 1, sbs, result);

28         }

29     }

30 }