Problem Description
Given a 32-bit signed integer, reverse digits of an integer.

Example 1:

Input: 123
Output: 321
Example 2:

Input: -123
Output: -321
Example 3:

Input: 120
Output: 21
Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [?231, 231 ? 1]. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

Java:

class Solution {
    public int reverse(int x) {
        if (x == Integer.MIN_VALUE) return 0;
        int flag = x > 0 ? 1 : -1;
        x *= flag;
        int res = 0;
        
        while (x != 0) {
            if ((Integer.MAX_VALUE - x%10)/10 < res) return 0;
            res = res*10 + x%10;
            x /= 10;
        }
        
        return res * flag;
    }
}