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Letter Combinations of a Phone Number

Question​

com

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.

Example 1
None

Solution​

all//Letter Combinations of a Phone Number.py


def letter_combinations(digits):
    if not digits:
        return []

    digits_map = {
        '2': 'abc',
        '3': 'def',
        '4': 'ghi',
        '5': 'jkl',
        '6': 'mno',
        '7': 'pqrs',
        '8': 'tuv',
        '9': 'wxyz'
    }
    result = []
    def backtrack(combination, next_digits):
        if len(next_digits) == 0:
            result.append(combination)
        else:
            for letter in digits_map[next_digits[0]]:
                backtrack(combination + letter, next_digits[1:])

    backtrack("", digits)
    return result