LeetCode-in-All

9. Palindrome Number

Easy

Given an integer x, return true if x is palindrome integer.

An integer is a palindrome when it reads the same backward as forward. For example, 121 is palindrome while 123 is not.

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:

• -231 <= x <= 231 - 1

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

Here are the steps to solve the “Palindrome Number” problem:

Approach:

1. Handle Special Cases for Negative Numbers:
   • If the given integer x is negative, return false since negative numbers cannot be palindromes.
2. Reverse the Integer:
   • Reverse the digits of the positive integer x to obtain a new integer.
3. Check for Palindrome:
   • Compare the reversed integer with the original integer x.
   • If they are equal, return true; otherwise, return false.
4. Return Result:
   • Return the result indicating whether the integer is a palindrome or not.

Python Code:

class Solution:
    def isPalindrome(self, x: int) -> bool:
        # Handle special case for negative numbers
        if x < 0:
            return False

        # Reverse the digits of the positive integer
        reversed_x = self.reverse(x)

        # Check for palindrome
        return x == reversed_x

    def reverse(self, x: int) -> int:
        reversed_x = 0
        while x > 0:
            digit = x % 10
            reversed_x = reversed_x * 10 + digit
            x //= 10
        return reversed_x

# Example Usage:
solution = Solution()

# Example 1:
x1 = 121
print(solution.isPalindrome(x1))  # Output: True

# Example 2:
x2 = -121
print(solution.isPalindrome(x2))  # Output: False

# Example 3:
x3 = 10
print(solution.isPalindrome(x3))  # Output: False

# Example 4:
x4 = -101
print(solution.isPalindrome(x4))  # Output: False

This code defines a Solution class with a method isPalindrome that takes an integer x as input and returns True if it is a palindrome and False otherwise. The example usage demonstrates how to create an instance of the Solution class and call the isPalindrome method with different inputs. The reverse method is used to reverse the digits of a positive integer.

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