Problem Statement:#

The largest palindrome formed by the product of two 2-digit numbers is 9009 = 99 × 91. Write a program to find the largest palindrome formed by the product of two n-digit numbers, where n is an arbitrary input. Input Format: A positive integer n Output Format: The largest palindrome formed by the product of two n-digit numbers Sample Input: 2 Sample Output: 9009

Program:

    def is_palindrome(num): 	#判断是否是回文
    	n = str(num)
    	if n == n[::-1]:
    		return True
    	else:
    		return False

    n = int(input())

    a = 1
    arr1 = []
    arr2 = []
    while len(str(a)) < n + 1: 		#将n位数的数字加到数组中，同时抛弃n-1位数
    	if len(str(a)) > n - 1:
    		arr1.append(a)
    		arr2.append(a)
    	a = a + 1

    maxPalindrome = 1
    for i in arr1[::-1]: 		#从后面往前开始遍历，取得最大的回文数
    	for j in arr2[::-1]:
    		if i*j > maxPalindrome and is_palindrome(i*j):
    			maxPalindrome = i*j
    print(maxPalindrome)

Summary#

I feel the algorithm is too brute-force and has low operational efficiency, but I haven’t thought of a better algorithm yet.