Problem

Given an integer x, return true if x is a

palindrome

, and false otherwise

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Palindrome
An integer is a palindrome when it reads the same forward and backward.

For example, 121 is a palindrome while 123 is not

.

Example 1:

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Input: x = 121
Output: true
Explanation: 121 reads as 121 from left to right and from right to left.

Example 2:

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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:

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

Constraints:

  • 2^31 <= x <= 2^31 - 1

Solve

利用字串

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class Solution:
    def isPalindrome(self, x: int) -> bool:
        str_x = str(x)
        r_str_x = str_x[::-1]
        if str_x == r_str_x:
            return True
        else:
            return False

簡化

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class Solution:
    def isPalindrome(self, x: int) -> bool:
        str_x = str(x)

        if str_x == str_x[::-1]:
            return True
        
        return False

數學

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class Solution:
    def isPalindrome(self, x: int) -> bool:
        if x < 0 or (x != 0 and x % 10 == 0):
            return False

        reversed_num = 0
        original = x

        while x > reversed_num:
            reversed_num = reversed_num * 10 + x % 10
            x //= 10

        return x == reversed_num or x == reversed_num // 10