判定一个正整数是否是一个回文数。例如12121是回文数，而1231不是回文数。回文数定义为可以以中间某个数字对称，或者间隔对称，例如123321，或者1234321。(Determines whether a positive integer is a palindrome. For example, 12121 is a palindrome, and 1231 is not a palindrome. Palindrome numbers are defined as symmetric or spaced symmetrically, such as 123321 or 1234321.)