题目描述

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:

Input: 121
Output: true

Example 2:

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

想法

• 想法一：把整数转换成字符串然后从中心往两边依次判断
• 想法二：把整数转过来，但是这会有一个问题就是反过来的数可能超过了int的范围
• 想法三：把整数的后半部分转过来，跟前半部分进行比较，那么这里就有一个问题就是如何判断整数已经到了一半，那就是从后面拿数拿出来的数比拿掉后的大了就已经达到了一半

代码

public boolean isPalindrome(int x) {
        if(x < 0 || (x % 10 == 0 && x != 0)) {
            return false;
        }
        int revertedNumber = 0;
        while(x > revertedNumber) {
            revertedNumber = revertedNumber * 10 + x % 10;
            x /= 10;
        }
        return x == revertedNumber || x == revertedNumber/10;
//可能是奇数也可能偶数
    }