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Grokking the Coding Interview Patterns in JavaScript

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 backtracking. Understand how to recursively generate all possible valid letter combinations from digits 2 to 9. This lesson guides you through the algorithm, its time and space complexity, and coding implementation to strengthen your problem-solving skills for coding interviews.

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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]

Pattern: Subsets

This problem lends itself naturally to the subsets pattern. To solve this problem, we can use a backtracking algorithm as the solution template to correctly generate all the possible combinations.

Solution

Since we need to explore different choices for each digit and generate valid combinations, we can use the subset technique with backtracking. It involves iterating through each ...