[LeetCode] Palindrome Number

题目

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

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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.

思路

之前已经实现了Reverse Integer，如果一个正数跟它反转后的数相等，那么这个数就是回文数。溢出情况就不需要考虑了。

代码

public class Solution {    public boolean isPalindrome(int x) {        if (x < 0)            return false;                long y = reverse((long)x);                return (x == y);    }        public long reverse(long x) {        long ret = 0, remain = x;                while (remain != 0){            ret = ret*10 + remain % 10;            remain /= 10;        }        return ret;    }}