Section 1Understand Problem
Section 01
Understand the problem
Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.
Problem statement
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.
Example
digits = "23" → ["ad","ae","af","bd","be","bf","cd","ce","cf"]
Constraints
0 ≤ digits.length ≤ 4 · digits[i] is in '2'..'9'
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