9. Palindrome Number

Leetcode

Determine whether an integer is a palindrome. Do this without extra space.

click to show spoilers.

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.

class Solution:
    def isPalindrome(self, x):
        if x < 0:
            return False

        r = 1
        while x / r >= 10:
            r *= 10

        while r > 1:
            left, x =divmod(x, r)
            x, right = divmod(x, 10)
            if left != right:
                return False
            r //= 100

        return True

//符号：

In Python 3
// => used for integer output
/ => used for double output

100/35 => 2.857142857142857
100//35 => 2
100.//35 => 2.0    # floating-point result if divsor or dividend real