Given a string input_digits consisting of digits from 2 to 9, return a list of all possible strings that can be formed by mapping each digit to its corresponding set of letters (as per the standard telephone keypad mapping). The order of the output list does not matter.
Example 1
Input: "34"
Output: [dg, dh, di, eg, eh, ei, fg, fh, fi]
Explanation: Digit 3 maps to [d,e,f], digit 4 maps to [g,h,i].
Example 2
Input: "7"
Output: [p, q, r, s]
Explanation: Digit 7 maps to [p,q,r,s].
Example 3
Input: "89"
Output: [ta, tb, tc, ua, ub, uc, va, vb, vc]
Explanation: Digit 8 maps to [t,u,v], digit 9 maps to [a,b,c].
Constraints
Case 1
Input: "56"
Expected: ['jm', 'jn', 'jo', 'km', 'kn', 'ko', 'lm', 'ln', 'lo']
Case 2
Input: "222"
Expected: ['aaa', 'aab', 'aac', 'aba', 'abb', 'abc', 'aca', 'acb', 'acc', 'baa', 'bab', 'bac', 'bba', 'bbb', 'bbc', 'bca', 'bcb', 'bcc', 'caa', 'cab', 'cac', 'cba', 'cbb', 'cbc', 'cca', 'ccb', 'ccc']
Case 3
Input: "5"
Expected: ['j', 'k', 'l']
Case 4
Input: "79"
Expected: ['pa', 'pb', 'pc', 'qa', 'qb', 'qc', 'ra', 'rb', 'rc', 'sa', 'sb', 'sc']