LeetCode-in-All
7. Reverse Integer
Medium
Given a signed 32-bit integer x, return x with its digits reversed. If reversing x causes the value to go outside the signed 32-bit integer range [-231, 231 - 1], then return 0.
Assume the environment does not allow you to store 64-bit integers (signed or unsigned).
Example 1:
Input: x = 123
Output: 321
Example 2:
Input: x = -123
Output: -321
Example 3:
Input: x = 120
Output: 21
Example 4:
Input: x = 0
Output: 0
Constraints:
-231 <= x <= 231 - 1
Solution
defmodule Solution do
@spec reverse(x :: integer) :: integer
def reverse(x) do
rev = reverse_digits(x, 0)
if rev > :math.pow(2, 31) - 1 or rev < -(:math.pow(2, 31)) do
0
else
rev
end
end
defp reverse_digits(0, acc), do: acc
defp reverse_digits(x, acc) do
new_acc = (acc * 10) + rem(x, 10)
reverse_digits(div(x, 10), new_acc)
end
end