9 Palindrome Number

题目链接：https://leetcode.com/problems/palindrome-number/

题目：

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.

解题思路：
有两种方式可以解决。
首先想到的是转换为字符串，然后从字符串两端向中间比较。
看了别人的答案才发现这是一道数学题。即，回文数字逆序后还是其本身。

注意：
负数不是回文， 0 是回文。

字符串方法：

public class Solution {public boolean isPalindrome(int x) {if(x < 0)return false;if(x / 10 == 0)return true;String num = Integer.toString(x);for(int i = 0; i <= num.length() / 2; i ++) {if(num.charAt(i) != num.charAt(num.length() - 1 - i))return false;}return true;}
}

11506 / 11506 test cases passed.
Status: Accepted
Runtime: 532 ms

整数转置方法：

public class Solution {public boolean isPalindrome(int x) {if(x < 0)return false;if(x / 10 == 0)return true;int num = x;int temp = 0;while(num != 0) {temp = temp * 10 + num % 10;num = num / 10;}if(temp == x)return true;elsereturn false;}
}

11506 / 11506 test cases passed.
Status: Accepted
Runtime: 532 ms

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