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Contents
defmodule Palindromes do
@doc """
Generates all palindrome products from an optionally given min factor (or 1) to a given max factor.
"""
@spec generate(non_neg_integer) :: map
@spec generate(non_neg_integer, non_neg_integer) :: map
def generate(max_factor, min_factor \\ 1) do
Enum.reduce(min_factor..max_factor, %{}, fn x, map ->
Enum.reduce(x..max_factor, map, fn y, products ->
if palindrome?(x * y), do: add_factor(products, x, y), else: products
end)
end)
end
defp palindrome?(number) do
String.reverse(to_string(number)) == to_string(number)
end
defp add_factor(map, x, y) do
product = x * y
Map.update(map, product, [[x, y]], fn val -> Enum.concat(val, [[x, y]]) end)
end
end
Version data entries
69 entries across 69 versions & 1 rubygems