Letter Combinations of a Phone Number

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Solve this the way you would in the interview: out loud, on a timer, with an AI interviewer asking follow-ups while you code. You get a scored report at the end.

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Problem

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 digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters. 2 → abc, 3 → def, 4 → ghi, 5 → jkl, 6 → mno, 7 → pqrs, 8 → tuv, 9 → wxyz

Examples

Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
Input: digits = ""
Output: []
Input: digits = "2"
Output: ["a","b","c"]

Constraints

  • 0 <= digits.length <= 4
  • digits[i] is a digit in the range ['2', '9'].

What the interviewer grades

A correct solution is one of five scores. The report also grades problem understanding (did you clarify inputs and edge cases before coding), problem solving, communication while you work, code quality, and testing. See a sample report, or read up on the pattern in the lessons.

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