# Letter Combinations Of A Phone Number

Letter Combinations Of A Phone Number backtracking

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.

``````2 - abc
3 - def
4 - ghi
5 - jkl
6 - mno
7 - pqrs
8 - tuv
9 - wxyz

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

Letter Combinations Of A Phone Number Solution

``````class LetterCombinationsOfAPhoneNumber {
public List<String> letterCombinations(String digits) {
List<String> result = new ArrayList<String>();

if(digits == null || digits.length() == 0) {
return result;
}

String[] mapping = {
"0",
"1",
"abc",
"def",
"ghi",
"jkl",
"mno",
"pqrs",
"tuv",
"wxyz"
};

letterCombinationsRecursive(result, digits, "", 0, mapping);

return result;
}

public void letterCombinationsRecursive(List<String> result, String digits, String current, int index, String[] mapping) {
if(index == digits.length()) {