import java.util.*;
import java.util.stream.*;
public class PalindromicNumber
{
public static void main(String[] args)
{
int result = largestPalindrome(3);
System.out.println("Result: " + result);
}
// Find the largest palindrome multiple of n-digit numbers
public static int largestPalindrome(int digits)
{
int result = Intstream.range(1, Math.pow(10, digits - 1))
.flatMap(a -> Intstream.range(1, Math.pow(10, digits - 1))
.map(b -> a * b)) // Multiples of n-digit numbers
.filter(n -> isPalindrome(n)) // Filter for palindromes
.reduce(0, (a, b) -> (a > b)? a : b); // Reduce for maximum
return result;
}
// Checks if number is palindromic
public static boolean isPalindrome(int number)
{
String numAsString = Integer.toString(number);
// Reverse number as a string
String reversed = new StringBuilder()
.append(numAsString)
.reverse()
.toString();
// If number is equal to reversed, it is a palindrome
return numAsString.equals(reversed);
}
}
This is an example of Java code I wrote for this class. This finds the largest palindromic
multiple of n digit numbers in a functional style. Using modern Java features helps make
my code more elegant and concise. Though this example code is in Java, I largely use C,
Javascript, or Python for my personal projects.
In this code, the isPalindrome(...) method, which determines if a
number is palindromic by comparing its string representation to its reversed string representation,
is used to filter through multiples of n-digit numbers in the largestPalindrome(...)
method.
