📌Problem

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

Follow up: Could you solve it without converting the integer to a string?

Example 1:

Input: x = 121
Output: true

Example 2:

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

Example 4:

Input: x = -101
Output: false

Constraints:

• $-2^{31}$ <= x <= $2^{31}$ - 1

leetcode 에서 풀기

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📝Solution

class Solution:
    def isPalindrome(self, x: int) -> bool:
        ret=None
        
        if x < 0:
            ret=False
        else:
            original=x
            reverse=0
            while x:
                remainder=x%10
                x=x//10
                reverse=reverse*10+remainder

            if reverse == original:            
                ret=True
            else:
                ret=False
        
        return ret

• Time complexity : $O(N)$

• x=12 , reverse=0

  quotient	remainder	reverse
  1	2	0*10+2=2
  0	1	2*10+1=21