LeetCode-in-All
17. Letter Combinations of a Phone Number
Medium
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 <= 4digits[i]is a digit in the range['2', '9'].
Solution
defmodule Solution do
@t9 (Enum.chunk_every(?a..?o, 3) ++ [~c"pqrs", ~c"tuv", ~c"wxyz"])
|> Enum.with_index(2)
|> Map.new(fn {a, n} -> {n, a} end)
@spec letter_combinations(digits :: String.t()) :: [String.t()]
def letter_combinations(""), do: []
def letter_combinations(digits) do
digits
|> String.to_integer()
|> Integer.digits()
|> Enum.map(&Map.get(@t9, &1))
|> Enum.reduce([~c""], fn l, acc ->
for x <- acc,
y <- l do
x ++ [y]
end
end)
|> Enum.map(&to_string/1)
end
end