9. Palindrome Number

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.

1 /** 2  * @param {number} x 3  * @return {boolean} 4  */ 5 var isPalindrome = function(x) { 6      7      8     //首先负数肯定不可以，然后就是120这种首位必然不同的 直接剪枝 9       if(x<0|| (x!=0 &&x%10==0)) return false;10         var sum=0;11     12     //这里直接将倒序的位数搞到和顺序的一半13         while(x>sum)14         {15             sum = sum*10+x%10;16             x = Math.floor(x/10);17         }18     19     //比较顺序一半长度和倒序的是不是相同20         return (x==sum)||(x==Math.floor(sum/10));21     22 };