LeetCode 7. Reverse Integer（反转整数）

题目网址：https://leetcode.com/problems/reverse-integer/description/

 

题目要求：

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.

算法思路：

 

• 定义一个整数变量result = 0
• 通过取余，每次获取一个个位数（tail）
• tail*10+result 即为反转后的数字
• 为了防止反转后的数字越界要判断反转后的数字/10 是否和原数相等

代码：

    /**
     * 反转整数
     * @param x 整数
     * @return 反转
     */
    public int reverse(int x) {
        int result =0;
        while (x != 0)
        {
            int tail = x%10;
            int newResult = result*10+tail;
            if((newResult - tail)/10 != result) {return 0;}
            result = newResult;
            x = x/10;
        }
        return result;
    }