LeetCode in Racket
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
(define/contract (reverse x)
(-> exact-integer? exact-integer?)
(let loop ((x x) (rev 0))
(if (= x 0)
(if (or (> rev (sub1 (expt 2 31))) (< rev (- (expt 2 31))))
0
rev)
(loop (quotient x 10) (+ (* rev 10) (remainder x 10))))))