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Grokking the Coding Interview Patterns in C++

Solution: Letter Combinations of a Phone Number

Explore how to solve the letter combinations of a phone number by using a backtracking approach within the subsets pattern. Understand how to generate all possible strings representing digit-to-letter mappings on a phone keypad. Learn to apply recursion and backtracking techniques to generate all valid combinations efficiently. This lesson equips you with problem-solving strategies essential for coding interviews involving similar combination and subset challenges.

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Statement

Given a string containing digits from 2 to 9 inclusive, with the possibility of each digit appearing multiple times, return all possible letter combinations that the number could represent. Return the answer in any order.

The illustration below shows the mapping of digits to letters in a telephone dial pad.

Note: The number 11 on the telephone dial pad does not correspond to any letter, so the input string only contains digits from 22 to 99.

Constraints:

  • 0≤0 \leq digits.length ≤4\leq 4

  • digits[i] is a digit in the range [2,9][2, 9] ...