Letter Combinations of a Phone Number(Problem Solving- Java)

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

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 1:

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

Example 2:

Input: digits = ""
Output: []

Example 3:

Input: digits = "2"
Output: ["a","b","c"]

Approach:

Lets take “23” as example, starting from left we will get letter combinations for each number in the input and associating each letter with the respective next number letter combination.

i=0 -> result=combine(“abc”, [“”]) — -> [a,b,c];

i=1 -> result=combine(“def”, [a,b,c]) — -> [ad,bd,cd, ae,be,ce, af,bf,cf];

Solution:

Iterative Solution:

public List<String> letterCombinations(String digits)
{
   ArrayList<String> result = new ArrayList<String>();
   ans.add("");  
   if(digits.length()==0) return result;
   String[] phone = new String[] {"0", "1", "abc", "def"…