Palindrome Number

A palindrome number reads the same forwards and backward. Identifying these numbers is a common programming challenge that can be solved efficiently using string manipulation and a two-pointer technique.

How it Works

To check if a number is a palindrome, the most straightforward approach involves converting the number into its string representation. This allows for character-by-character comparison, which is essential for palindrome detection.

First, any negative number cannot be a palindrome, as the negative sign breaks the symmetry. Such numbers can be immediately identified and result in `False`.

Once converted to a string, two pointers are initialized: one at the beginning of the string (left pointer, `l`) and one at the end (right pointer, `r`). These pointers then move towards the center of the string.

Comparing Characters

In each step, the characters at the positions indicated by `l` and `r` are compared. If the characters do not match at any point, the number is not a palindrome, and the process can stop, returning `False`.

If the characters match, both pointers are moved inwards: `l` increments and `r` decrements. This continues until the left pointer crosses or meets the right pointer (`l >= r`).

Determining the Result

If the loop completes without finding any mismatched characters, it means all corresponding pairs of characters from the beginning and end of the string were identical. In this case, the number is a palindrome, and the function returns `True`.

function is_palindrome(x):
  if x < 0: return false
  s = string(x)
  l = 0
  r = length(s) - 1
  while l < r:
    if s[l] != s[r]:
      return false
    l = l + 1
    r = r - 1
  return true

Key Takeaways

• Negative numbers are not palindromes.
• Converting the number to a string simplifies character comparison.
• A two-pointer approach efficiently compares characters from both ends.
• The process stops early if a mismatch is found.
• If all characters match, the number is a palindrome.