Leetcode 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

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. 

方法一：调包 

public int reverse(int x) {
        int xTmp = x;
        if (x < 0) xTmp = -x;
        StringBuilder sb = new StringBuilder(String.valueOf(xTmp));
        sb.reverse();
        int res = 0;
        try {
            res = Integer.parseInt(sb.toString());
        } finally {
            return x < 0 ? -res : res;
        }
}

方法二：数学知识

代码 todo