Leet Code 9 Palindrome Number

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.

【算法思路】
1. 简单粗暴，但是其实利用了多余的空间，因为把int转换为string的时候需要额外的空间。

public boolean isPalindrome(int x) {
if(x < 0)
{
return false;
}
if(x < 10 && x > 0)
{
return true;
}
return (new StringBuilder(String.valueOf(x)).reverse().toString().equals(String.valueOf(x)));
}

2. 对于数字的题目经常使用 / %。不断地取第一位和最后一位（10进制下）进行比较，相等则取第二位和倒数第二位，直到完成比较或者中途找到了不一致的位。

public boolean isPalindrome(int x) {
//negative numbers are not palindrome
if (x < 0)
return false;

// initialize how many zeros
int div = 1;
while (x / div >= 10) {
div *= 10;
}

while (x != 0) {
int left = x / div;
int right = x % 10;

if (left != right)
return false;

x = (x % div) / 10;
div /= 100;
}

return true;
}