LeetCode in Erlang
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
-spec reverse(X :: integer()) -> integer().
reverse(X) -> reverse(X, 0).
reverse(0, Work) ->
case abs(Work) > 2147483647 of
true -> reverse(0,0);
false -> Work
end;
reverse(X, Work) -> reverse(trunc(X/10), (Work*10) + X rem 10).