nonpalindromic

Nonpalindromic is an adjective describing any word, phrase, sequence, or number that is not a palindrome. A palindrome reads the same forward and backward, ignoring or including punctuation and spacing depending on the convention. By definition, nonpalindromic items fail to show this symmetry.

In language use, most ordinary words are nonpalindromic. For example, "example" and "nonpalindromic" itself are not palindromes. In phrases, palindrome checking often ignores spaces and punctuation, which can change whether a string is considered palindromic.

In mathematics and computer science, a nonpalindromic number has a decimal representation that is not the same when digits are reversed (e.g., 1234 vs 4321). Single-digit numbers are palindromic; two- or more-digit numbers may be nonpalindromic (e.g., 1221 is palindromic, 1234 is not).

Algorithmically, detecting nonpalindromicity typically involves comparing characters from opposite ends of a string and stopping at the first mismatch, yielding O(n) time and O(1) space. If no mismatch occurs, the string is palindromic; otherwise, it is nonpalindromic.

See also: palindrome, semordnilap, symmetry.