Closest Palindrome | Dataford Interview Questions

The Uber Drivers app occasionally formats numeric values such as driver-facing trip references in a way that benefits from a nearby palindromic value. Given a positive integer as a decimal string, return the closest different positive-or-zero palindrome.

If two palindromes are equally close, return the smaller one.

Formal Specification

Implement closest_palindrome(n), where n is a decimal string with no leading zeros unless n is "0". Return a decimal string representing the palindrome p that minimizes abs(int(n) - int(p)), subject to p != n.

The result may be "0". You may use integer arithmetic within the stated constraints.

Constraints

1 <= len(n) <= 18
n contains only decimal digits
n has no leading zeros unless it is "0"
The input represents a non-negative integer
The answer must be different from the input

Function Signature

def closest_palindrome(n):

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Problem