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.

方法1： reverse 输入，看结果是否相等，注意reverse后可能溢出

方法2： 不断比较最高位和最低位，如果相等减掉最高位和最低位，最低位直到0；

 

public class Solution {
        public static boolean isPalindrome(int x) {
         if(x < 0) return false;
         
         int scale = 1;
         int tmp = x;
         
         while(tmp / 10 > 0){
             scale = scale*10; // 计算 x 的位数； eg: x = 123; scale = 100
             tmp = tmp /10; 
         }
         
         while(x > 0){
             int front = x / s;
             int end = x % 10;
             if(front != end){
                 return false;
             }
             
             x = x - front*scale;
             x = x - end;
             x = x /10;
             // 因为头尾各减掉一位 共两位
             scale = scale / 100;
         }
         
         return true;
         
        }
}