7. Reverse Integer

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

//Time: O(n), Space:O(1)  
 public int reverse(int x) {
        long result = 0;//为了防止溢出，用long来hold
        while (x != 0) { //无所谓正负
            result = result * 10 + x % 10;
            if (result > Integer.MAX_VALUE || result < Integer.MIN_VALUE) {
                return 0;
            }
            x = x / 10;
        }
        return (int) result;
    }