Closest Palindrome Number (absolute difference Is min)

// Java program to find the closest
// Palindrome number
import java.io.*;

class GFG {

    // Function to check Palindrome
    public static boolean isPalindrome(String s)
    {
        int left = 0;
        int right = s.length() - 1;

        while (left < right) {
            if (s.charAt(left) != s.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }

    // Function return closest Palindrome number
    public static void closestPalindrome(int num)
    {

        // Case1 : largest palindrome number
        // which is smaller to given number
        int RPNum = num - 1;

        while (isPalindrome(Integer.toString(RPNum))
               == false) {
            RPNum--;
        }

        // Case 2 : smallest palindrome number
        // which is greater than given number
        int SPNum = num + 1;

        while (isPalindrome(Integer.toString(SPNum))
               == false) {
            SPNum++;
        }

        // Check absolute difference
        if (Math.abs(num - SPNum) < Math.abs(num - RPNum)) {
            System.out.println(SPNum);
        }
        else
            System.out.println(RPNum);
    }

    // Driver code
    public static void main(String[] args)
    {
        int n = 121;

        closestPalindrome(n);
    }
}

// This code is contributed by kes333hav

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class ClosestPalindrome {

    public static String closestPalindrome(String n) {
        // Initialize a list to store the candidate palindromic numbers
        List<Long> candidates = new ArrayList<>();

        // Get the length of the input number n
        int length = n.length();

        // Calculate the index of the middle element (or the element just after the middle for even-length numbers)
        int mid = (length + 1) / 2;

        // If the input number has only one digit, the closest palindromic number is (n-1)
        if (length == 1) {
            long num = Long.parseLong(n);
            return String.valueOf(num - 1);
        }

        // Add two candidates: (10^n + 1) and (10^(n-1) - 1)
        candidates.add((long) Math.pow(10, length) + 1);
        candidates.add((long) Math.pow(10, length - 1) - 1);

        // Extract the prefix (first half) of the input number
        int prefix = Integer.parseInt(n.substring(0, mid));

        // Generate three possible prefixes by incrementing and decrementing the original prefix
        List<Integer> temp = Arrays.asList(prefix, prefix + 1, prefix - 1);

        // Construct the candidate palindromic numbers using the generated prefixes
        for (int i : temp) {
            String res = String.valueOf(i);
            // If the length of the input number is odd, exclude the last character while constructing the palindromic number
            if ((length & 1) != 0) {
                res = res.substring(0, res.length() - 1);
            }
            // Create the palindromic number by appending the reverse of the prefix
            String peep = i + new StringBuilder(res).reverse().toString();
            candidates.add(Long.parseLong(peep));
        }

        // Initialize variables to keep track of the minimum difference and the closest palindromic number
        long minDiff = Long.MAX_VALUE;
        long result = Long.parseLong(n);
        long tip = Long.parseLong(n);

        // Iterate through the candidate palindromic numbers and find the closest one to the input number
        for (int i = 0; i < 5; i++) {
            long candidate = candidates.get(i);
            if (candidate != tip && minDiff > Math.abs(candidate - tip)) {
                result = candidate;
                minDiff = Math.abs(candidate - tip);
            } else if (Math.abs(candidate - tip) == minDiff) {
                result = Math.min(result, candidate);
            }
        }

        return String.valueOf(result);
    }

    public static void main(String[] args) {
        String num = "489";
        System.out.println(closestPalindrome(num));
    }
}

// This code is contributed by shivamgupta0987654321