Medium · Backtracking
Letter Combinations of a Phone Number
Given a string digits made of the characters '2'–'9', return every letter string it could spell on a phone keypad (2 → abc, 3 → def, 4 → ghi, 5 → jkl, 6 → mno, 7 → pqrs, 8 → tuv, 9 → wxyz), in any order; if digits is empty, return an empty list.
Examples
Example 1
digits = "23"Output: 9 combos
Example 2
digits = "2"Output: 3 combos
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