LeetCode-in-All

9. Palindrome Number

Easy

Given an integer x, return true if x is palindrome integer.

An integer is a palindrome when it reads the same backward as forward. For example, 121 is palindrome while 123 is not.

Example 1:

Input: x = 121

Output: true

Example 2:

Input: x = -121

Output: false

Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: x = 10

Output: false

Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Example 4:

Input: x = -101

Output: false

Constraints:

Follow up: Could you solve it without converting the integer to a string?

Solution

defmodule Solution do
  @spec is_palindrome(x :: integer) :: boolean
  def is_palindrome(x) when x < 0, do: false
  def is_palindrome(x) when x < 10, do: true
  def is_palindrome(x) do
    reversed = x
    |> Integer.digits
    |> Enum.reverse
    |> Integer.undigits

    x == reversed
  end
end