009 Palindrome Number

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

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• 要求：
  判断所给整数是否是回文。
  • 能否不转化成string做出

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• 返回： True/False

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• 例子：
  • input: 121
  • output: True

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Solution

利用math.log()将整数逐位表示，再反向读取，判断反向后的数是否和原数相等。

class Solution:
    def isPalindrome(self, x):
        """
        :type x: int
        :rtype: bool
        """
        
        ## didn't use string
        import math
        if x<0:
            return False
        elif x>=0  and x<=9:
            return True
        else:
            num_digits  = math.ceil(math.log(x, 10))
            digits = [(x//(10**i))%10 for i in range(num_digits-1, -1, -1)]
			
			# read integer backwards
            r = 0
            for i in range(len(digits)):
                r += digits[-(i+1)]*(10**(num_digits-i-1))  
            if r == x:
                return True
            else:
                return False