题目：

Given a group of two strings, you need to find the longest uncommon subsequence of this group of two strings. The longest uncommon subsequence is defined as the longest subsequence of one of these strings and this subsequence should not be any subsequence of the other strings.

A subsequence is a sequence that can be derived from one sequence by deleting some characters without changing the order of the remaining elements. Trivially, any string is a subsequence of itself and an empty string is a subsequence of any string.

The input will be two strings, and the output needs to be the length of the longest uncommon subsequence. If the longest uncommon subsequence doesn‘t exist, return -1.

给两个字符串，最长子序列是其中一个字符串的子序列而不是另一个字符串的子序列，字符串的子序列可以通过删除一些字符而不改变其余元素的顺序来从一个序列中派生出来，一般来说，任何字符串都是它自身的子序列而空字符串是任何字符串的子序列。求最长子序列长度。如果最长的子序列不存在，则返回-1。

思路：想了半天，原来是脑筋急转弯，如果两个元素不等长，那么其中长字符本身就不是另一个字符的子序列，输出长度就行，如果等长，那么如果两个字符串相同，返回-1，不同返回长度，因为一个不是另一个的子序列。

就是说如果两个字符串相同就返回-1，不同就返回最长的

结果：

class Solution(object):
    def findLUSlength(self, a, b):
        """
        :type a: str
        :type b: str
        :rtype: int
        """
        if a == b:
            return -1
        else:
            return max(len(a),len(b))

521. Longest Uncommon Subsequence I （最长不寻常子序列） by Python