Letter Combinations of a Phone Number

Medium · Backtracking

You are given a string of digits between 2 and 9, like an old phone keypad input. Each digit maps to a set of letters, the same way it did on classic phone keypads (2 is abc, 3 is def, and so on, with 7 mapping to qprs and 8 to tuv). Return every possible letter combination you could make by choosing one letter for each digit in order. If the input string is empty, return no combinations at all.

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Practise Letter Combinations of a Phone Number

This statement is written for CodeSpeek. The problem is part of the NeetCode 150 list; Watch NeetCode's explanation of Letter Combinations of a Phone Number. Reference solutions from the NeetCode repository (MIT) are used to verify our tests.