Check if a number with even number of digits is palindrome or not

A palindrome is a number that reads the same forwards and backwards. This article shows how to check if a number with an even number of digits is a palindrome in Python. Examples include 2662, 4224, 44, 1001, etc.

Using String Comparison

The simplest approach converts the number to a string and compares it with its reverse ?

def is_even_digit_palindrome(num):
    # Convert number to string
    num_str = str(num)
    
    # Check if even number of digits
    if len(num_str) % 2 != 0:
        return False
    
    # Check if palindrome
    return num_str == num_str[::-1]

# Test with even digit numbers
numbers = [2662, 4224, 44, 1001, 123321, 12321]

for num in numbers:
    result = is_even_digit_palindrome(num)
    digit_count = len(str(num))
    print(f"{num} ({digit_count} digits): {'Palindrome' if result else 'Not palindrome'}")

2662 (4 digits): Palindrome
4224 (4 digits): Palindrome
44 (2 digits): Palindrome
1001 (4 digits): Palindrome
123321 (6 digits): Palindrome
12321 (5 digits): Not palindrome

Using Mathematical Approach

This method reverses the number mathematically without string conversion ?

def reverse_number(num):
    """Reverse a number mathematically"""
    reversed_num = 0
    while num > 0:
        reversed_num = reversed_num * 10 + num % 10
        num //= 10
    return reversed_num

def count_digits(num):
    """Count number of digits in a number"""
    if num == 0:
        return 1
    count = 0
    while num > 0:
        count += 1
        num //= 10
    return count

def is_even_digit_palindrome_math(num):
    # Count digits
    digit_count = count_digits(num)
    
    # Check if even number of digits
    if digit_count % 2 != 0:
        return False
    
    # Check if palindrome
    return num == reverse_number(num)

# Test the mathematical approach
test_numbers = [2662, 4224, 44, 1001, 8888]

for num in test_numbers:
    result = is_even_digit_palindrome_math(num)
    digits = count_digits(num)
    print(f"{num} ({digits} digits): {'Even-digit palindrome' if result else 'Not even-digit palindrome'}")

2662 (4 digits): Even-digit palindrome
4224 (4 digits): Even-digit palindrome
44 (2 digits): Even-digit palindrome
1001 (4 digits): Even-digit palindrome
8888 (4 digits): Even-digit palindrome

Finding All Even-Digit Palindromes in a Range

This function generates all even-digit palindromes within a specified range ?

def find_even_digit_palindromes(start, end):
    """Find all even-digit palindromes in a range"""
    palindromes = []
    
    for num in range(start, end + 1):
        num_str = str(num)
        
        # Check if even number of digits and palindrome
        if len(num_str) % 2 == 0 and num_str == num_str[::-1]:
            palindromes.append(num)
    
    return palindromes

# Find even-digit palindromes between 1 and 10000
palindromes = find_even_digit_palindromes(10, 10000)
print(f"Even-digit palindromes between 10 and 10000:")
print(f"Total found: {len(palindromes)}")
print(f"First 20: {palindromes[:20]}")

Even-digit palindromes between 10 and 10000:
Total found: 108
First 20: [11, 22, 33, 44, 55, 66, 77, 88, 99, 1001, 1111, 1221, 1331, 1441, 1551, 1661, 1771, 1881, 1991, 2002]

Comparison of Methods

Conclusion

Use string comparison for simplicity and readability. The mathematical approach is more memory-efficient for large numbers. Both methods effectively check if a number with an even digit count is a palindrome.