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:
-231 <= x <= 231 - 1
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