（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
--
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※ wheels:轉錄至看板 Soft_Job 12/08 16:23
※ 編輯: wheels (60.245.65.132 臺灣), 12/08/2019 19:06:07