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.

 

 1 public class Solution {

 2     public boolean isPalindrome(int x) {

 3         // Note: The Solution object is instantiated only once and is reused by each test case.

 4         if(x < 0) return false;

 5         int len = 0;

 6         int xx = x;

 7         while(xx > 0){

 8             len ++;

 9             xx = xx / 10;

10         }

11         for(int i = 0; i < len / 2; i ++){

12             int a = (x / (int)Math.pow(10, i)) % 10;

13             int b = (x / (int)Math.pow(10, len - i - 1)) % 10;

14             if(a != b) return false;

15         }

16         return true;

17     }

18 }

 第三遍：

 1 public class Solution {

 2     public boolean isPalindrome(int x) {

 3         if(x < 0) return false;

 4         int num = 0;

 5         while(x >= Math.pow(10, num)) num ++;

 6         for(int i = 0; i < num / 2; i ++){

 7             int aa = x / (int)(Math.pow(10, num - i - 1)) % 10;

 8             int bb = x / (int)(Math.pow(10, i)) % 10;

 9             if(aa != bb) return false;

10         }

11         return true;

12     }

13 }