Letter Combinations of a Phone Number

Given a string of digits from 2 to 9, return every possible letter combination it could represent using the classic phone keypad mapping. A standard backtracking exercise with follow-ups on recursion structure versus iterative generation. Letter Combinations of a Phone Number Given a string of digits from 2 to 9, return every possible letter combination it could represent using the classic phone keypad mapping. A standard backtracking exercise with follow-ups on recursion structure versus iterative generation. SWE medium backtracking recursion string Frequency Low Last asked 2026-03-15 Stage onsite-coding Letter Combinations of a Phone Number Given a string digits containing digits from 2 to 9, return every possible letter combination the number could represent. Use the classic phone keypad mapping where 2 maps to "abc", 3 maps to "def", 4 maps to "ghi", 5 maps to "jkl", 6 maps to "mno", 7 maps to "pqrs", 8 maps to "tuv", and 9 maps to "wxyz". Return the combinations in any order. If digits is empty, return an empty array. Examples Example 1: Input: digits = "23" Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"] Example 2: Input: digits = "" Output: [] Example 3: Input: digits = "7" Output: ["p","q","r","s"] Constraints 0 <= digits.length <= 4 digits[i] is a digit in the range ["2", "9"]. Notes Expect a follow-up discussion comparing the recursive backtracking structure against an iterative generation approach.