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Grokking the Coding Interview Patterns in Go

Solution: Letter Combinations of a Phone Number

Explore the backtracking technique to solve the letter combinations of a phone number problem. This lesson helps you understand how to recursively generate all valid letter combinations for digit sequences, applying subset patterns commonly asked in coding interviews. You'll learn to handle edge cases, use recursion effectively, and analyze the time and space complexity of the solution.

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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] ...