17. Letter Combinations of a Phone Number

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

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

Example 1:

Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]

Example 2:

Input: digits = ""
Output: []

Example 3:

Input: digits = "2"
Output: ["a","b","c"]

Constraints:

• 0 <= digits.length <= 4
• digits[i] is a digit in the range ['2', '9'].

# @lc code=start
using LeetCode

function letter_combinations(digits::String)::Vector{String}
    isempty(digits) && return String[]
    table = Dict{Char,String}(
        '2' => "abc",
        '3' => "def",
        '4' => "ghi",
        '5' => "jkl",
        '6' => "mno",
        '7' => "pqrs",
        '8' => "tuv",
        '9' => "wxyz",
    )
    res = [""]
    for i in digits
        res = [s1 * s2 for s1 in res for s2 in table[i]]
    end
    return res
end
# @lc code=end

letter_combinations (generic function with 1 method)

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