3rd LeetCode: Letter Combinations of a Phone Number

Solution1

K digits form 2~9 represent a~z

Return all possible combinations of letters that that input K digits in the range of 2~9 can represent. For example, input 2 digits “45” could mean: ‘gj’, ‘gk’, ‘gl’, ‘hj’, ‘hk’, ‘hl’, ‘ij’, ‘ik’, ‘il’.

The solution is straight forward: decode each digit k for the possible letter(k)

1. Create a function letter(digit) to produce possible letters for that digit:
   Map “2” to “abc”, ”3” to “def”, “4” to “ghi”,… and so on.
2. Gain all possible letters according to input digits by function described in 1.
3. Create a recursive function listing all the possible combination of letters (i.e., words):
   a. Pick one from each mapped letter sets generated by the digits and store this combination to the list.
   b. Try a different combination and store to the list, and so on.
4. Return the list

https://leetcode.com/problems/letter-combinations-of-a-phone-number/discuss/602936/Python-3-recursive-mathod-with-code-mapping