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Grokking the Coding Interview Patterns in Go

Solution: Letter Combinations of a Phone Number

Explore how to generate all possible letter combinations from phone number digits using a backtracking approach based on the subsets pattern. Understand the recursive process to build combinations, handle backtracking, and analyze time and space complexity. This lesson helps you apply this pattern to similar coding problems efficiently.

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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] ...