計算數學 Problem Solving- Leetcode 294 Flip Game II

（更新）發現是 Leetcode 的 test case 不夠完整造成的誤會，感謝收看。

因為是鎖起來的題目所以直接貼：

You are playing the following Flip Game with your friend:

Given a string that contains only these two characters: + and -,
you and your friend take turns to flip two consecutive '++' into '--'.

The game ends when a person can no longer make a move and
therefore the other person will be the winner.

Write a function to determine if the starting player can guarantee a win.

Example:
Input: s = '++++'

Output: true
Explanation: The starting player can guarantee a win by flipping the middle
'++' to become '+--+'.

Follow up:
Derive your algorithm's runtime complexity.


這題我有用 recursion + memo 解出來，

但看到一個 finding pattern 的方法可以 AC 且 100%，

不過卻無法參透它，想請問有沒有人可以幫忙說明下，感激不盡。

# Python3
class Solution:
def canWin(self, s: str) -> bool:
S, length = set(), 0
for c in s + '-':
if c == '-':
if length and length % 4 != 1:
length |= 1
S ^= {length}
length = 0
else:
length += 1
return S

--