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🔥Letter Combinations of a Phone Number: T9 KeyboardMedium
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MediumArrays & Hashing•Acceptance: 60.4%

Letter Combinations of a Phone Number: T9 Keyboard

Targeted in FAANG & Tech OA:AmazonMicrosoftUber
Real-World Engineering Context
Used in T9 predictive keyboard typing, vanity phone number generators (e.g. 1-800-FLOWERS), and mnemonic encoding systems.
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 telephone buttons): - 2: 'abc', 3: 'def', 4: 'ghi', 5: 'jkl', 6: 'mno', 7: 'pqrs', 8: 'tuv', 9: 'wxyz'.

Sample Test Cases

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

Constraints

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