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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 problem by applying the subsets pattern with a backtracking approach. This lesson helps you generate all valid letter combinations from digit sequences efficiently, understand recursive backtracking techniques, and analyze time and space complexity in C#. Gain practical skills to tackle similar coding interview questions.

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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] ...