沙盒

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defmodule Solution do
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  @spec is_palindrome(x :: integer) :: boolean
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  def is_palindrome(x) when x < 0, do: false
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  def is_palindrome(x), do: do_is_palindrome(x, get_base_10(x, 1))
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  defp do_is_palindrome(x, b10) when b10 > 1,
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    do: get_first_digit(x, b10) == rem(x, 10) and do_is_palindrome(div(x, 10), div(b10, 100))
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  defp do_is_palindrome(_, _), do: true
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  defp get_first_digit(n, b10), do: div(n, b10) |> rem(10)
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  defp get_base_10(n, b10) when n >= b10, do: get_base_10(n, b10 * 10)
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  defp get_base_10(n, b10), do: div(b10, 10)
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end