Palindrome Number

题目描述

Determine whether an integer is a palindrome. Do this without extra space.

Some hints:

Could negative integers be palindromes? (ie, -1)

If you are thinking of converting the integer to string, note the restriction of using extra space.

You could also try reversing an integer. However, if you have solved the problem "Reverse Integer", you know that the reversed integer might overflow. How would you handle such case?

There is a more generic way of solving this problem.

判断数字是不是回文数字。

解题思路

不能用额外的空间，所以不能用字符串或数组。

可以用一个 long 去计算翻转后的数字是否和原数字相等。

• 负数全部是 false；
• 超出范围是 false；
• 不相等是 false；
• 相等时 true。

代码

class Solution {
    public boolean isPalindrome(int x) {
        if (x < 0)
            return false;
        long ret = 0;
        int tmp = x;
        do {
            ret *= 10;
            ret = ret + x % 10;
            x /= 10;
            if (ret > Integer.MAX_VALUE || ret < Integer.MIN_VALUE)
                return false;
        } while (x != 0);
        return tmp == ret;
    }
}