[LeetCode] 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.

 

每次，取出数的最高位和最低位比较，这里设置一个base为10^n，用来取出数的最高位，每次循环除以100，因为每次数会消去2位。

 1 class Solution {

 2 public:

 3     bool isPalindrome(int x) {

 4         // Start typing your C/C++ solution below

 5         // DO NOT write int main() function

 6         if (x < 0)

 7             return false;

 8         if (x == 0)

 9             return true;

10             

11         int base = 1;

12         while(x / base >= 10)

13             base *= 10;

14             

15         while(x)

16         {

17             int leftDigit = x / base;

18             int rightDigit = x % 10;

19             if (leftDigit != rightDigit)

20                 return false;

21             

22             x -= base * leftDigit;

23             base /= 100;

24             x /= 10;

25         }

26         

27         return true;

28     }

29 };