#17

Letter Combinations of a Phone Number

medium· Backtrackingruns: 0

Given a string containing digits from 2 to 9 inclusive, return all possible letter combinations that the number could represent. A standard mapping of digits to letters (like a phone keypad) is used; 1 does not map to any letters.

wpm 0acc 100%time 0:000 / 700

class Solution:
    def letterCombinations(self, digits: str) -> list[str]:
        if not digits:
            return []
        mapping = {
            "2": "abc",
            "3": "def",
            "4": "ghi",
            "5": "jkl",
            "6": "mno",
            "7": "pqrs",
            "8": "tuv",
            "9": "wxyz",
        }
        result = []
        path = []

        def backtrack(i: int) -> None:
            if i == len(digits):
                result.append("".join(path))
                return
            for c in mapping[digits[i]]:
                path.append(c)
                backtrack(i + 1)
                path.pop()

        backtrack(0)
        return result

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