最大回文数乘积

// Problem Statement: Find the largest palindrome made from the product of two n-digit numbers. Return the result modulo 1337.
// 
// Approach with Java Streams:
// 1. Use streams to generate numbers and filter the pairs.
// 2. For each pair, calculate the product and check for palindrome.
// 3. Find the maximum palindrome and return the result modulo 1337.
 
import java.util.stream.IntStream;
 
public class Solution {
    public int largestPalindrome(int n) {
        if (n == 1) return 9;
        int upperLimit = (int) Math.pow(10, n) - 1;
        int lowerLimit = (int) Math.pow(10, n - 1);
        int maxPalindrome = IntStream.rangeClosed(lowerLimit, upperLimit).boxed()
            .flatMap(i -> IntStream.rangeClosed(lowerLimit, i).mapToObj(j -> i * j))
            .filter(Solution::isPalindrome)
            .max(Integer::compare)
            .orElse(0);
        return maxPalindrome % 1337;
    }
 
    private static boolean isPalindrome(int num) {
        int original = num;
        int reversed = 0;
        while (num > 0) {
            reversed = reversed * 10 + num % 10;
            num /= 10;
        }
        return original == reversed;
    }
}