# Palindrome Number

## Problem

### Description

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

click to show spoilers.

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.

## 题解1 - 循环处理首尾数字

### Java

class Solution {
public boolean isPalindrome(int x) {
if (x < 0) return false;

int mod = 1000000000;
while (x / mod == 0 && (mod > 1)) {
mod /= 10;
}
while (mod > 1) {
if (x / mod != x % 10) {
return false;
}
x = (x % mod) / 10;
mod /= 100;
}
return true;
}
}


## 题解2 - 逆序比对

### Java

class Solution {
public boolean isPalindrome(int x) {
if (x < 0) return false;

int prev = 0;
int y = x;
while (y > 0) {
prev = prev * 10 + y % 10;
y /= 10;
}
if (prev == x) {
return true;
} else {
return false;
}
}
}