Palindrome in Python: How to check a number is palindrome?

A palindrome is a string that reads the same forwards and backwards. In other words, a palindrome string is equal to its reverse.

For example, "civic" and "madam" are palindromes, while "cat" is not (its reverse "tac" differs from the original).

Method 1: Using String Slicing

The simplest approach is to reverse the string using slicing and compare it with the original ?

def isPalindrome(s):
    rev = s[::-1]
    if rev == s:
        return True
    return False

text = "madam"
print(f"'{text}' is palindrome:", isPalindrome(text))

text = "hello"
print(f"'{text}' is palindrome:", isPalindrome(text))

'madam' is palindrome: True
'hello' is palindrome: False

Method 2: Using Two Pointers

This approach compares characters from both ends moving inward, without creating a reversed string ?

def isPalindrome(s):
    start = 0
    end = len(s) - 1
    
    while start < end:
        if s[start] != s[end]:
            return False
        start += 1
        end -= 1
    
    return True

text = "madam"
print(f"'{text}' is palindrome:", isPalindrome(text))

text = "reader"  
print(f"'{text}' is palindrome:", isPalindrome(text))

'madam' is palindrome: True
'reader' is palindrome: False

Method 3: Checking Numeric Palindromes

For numbers, convert to string first or use mathematical operations ?

def isNumericPalindrome(num):
    # Convert to string and check
    return str(num) == str(num)[::-1]

def isNumericPalindromeByMath(num):
    # Using mathematical approach
    original = num
    reversed_num = 0
    
    while num > 0:
        reversed_num = reversed_num * 10 + num % 10
        num //= 10
    
    return original == reversed_num

number = 12321
print(f"{number} is palindrome:", isNumericPalindrome(number))

number = 12345
print(f"{number} is palindrome:", isNumericPalindromeByMath(number))

12321 is palindrome: True
12345 is palindrome: False

Comparison

Conclusion

Use string slicing for simplicity, two pointers for memory efficiency, and mathematical approach for numeric palindromes. The two-pointer method is most optimal for large strings.