LeetCode #9 - Palindrome Number - Easy

Problem

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.

Example

Input：-2147483648Output：flase

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Algorithm

整理一下题意：给定一个整数，判断其是否是回文数。要求不使用额外空间。

由于对空间使用有限制，所以要控制空间复杂度为O(1)。于是很自然地想到利用回文数的性质。回文数的特点在于数字可以形成对称，于是将这个数反过来还是和原来的数相等。于是只要开两个变量来得到翻转后的数字，再将翻转后的数字与原数比较即可。

注意负数均不是回文数。

代码如下。

class Solution {public:    bool isPalindrome(int x) {        if(x<0) return false;        int temp=x,reverse=0;        while(temp){            reverse=reverse*10+temp%10;            temp/=10;        }        if(reverse==x)return true;        else return false;    }};