leetcode 9. Palindrome Number

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1:

Input: 121
Output: true

Example 2:

Input: -121
Output: false
Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: 10
Output: false
Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Follow up:

Coud you solve it without converting the integer to a string?

class Solution(object):
    def isPalindrome(self, x):
        """
        :type x: int
        :rtype: bool
        """
        if x < 0: return False
        s = str(x)
        i, j = 0, len(s)-1
        while i<j:
            if s[i] != s[j]:
                return False
            i += 1
            j -= 1
        return True

不使用string的话，还是比较巧妙的：

class Solution(object):
    def isPalindrome(self, x):
        """
        :type x: int
        :rtype: bool
        """
        if x < 0: return False
        num = x
        y = 0
        while x != 0:
            y = y*10 + x%10
            x /= 10
        return y == num