Palindromechecking

Palindromechecking is the process of determining whether a given sequence reads the same forwards and backwards. This can apply to strings, numbers, arrays, or other ordered data. In many contexts the check is performed on exact characters, but variants often ignore case, spaces, or punctuation to treat phrases as palindromes.

Common algorithms start with a two-pointer approach. One pointer begins at the start of the sequence and the other at the end; the elements they point to are compared and the pointers move toward the center. If all corresponding elements match, the sequence is a palindrome; a single mismatch means it is not. This method runs in linear time with constant extra space, O(n) time and O(1) space, assuming direct access to elements. An alternative is to reverse a copy of the sequence and compare it to the original; this is typically O(n) time and O(n) space.

Variations of palindromechecking depend on the definition used. For strings, case sensitivity matters unless normalized, and handling of non-alphanumeric characters varies by application. In phrase palindromes, spaces and punctuation are often ignored, and Unicode normalization may be required to handle accented characters correctly. For numeric palindromes, checks usually involve digits only and may require avoiding leading zeros or signs, depending on the specification. In computational settings, algorithms can be implemented iteratively or recursively, though recursion may incur overhead for long sequences.

Applications include input validation, pattern matching, and educational examples in algorithm design. Related concepts include palindrome numbers, full-string palindrome checks, and more specialized ideas in biology and data processing where symmetry or reverse-complement properties are relevant.