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.
class Solution:
def canWin(self, s):
"""
:type s: str
:rtype: bool
"""
for i in range(len(s) - 1):
if s[i:i + 2] == "++":
if not self.canWin(s[:i] + "--" + s[i + 2:]):
return True
return False
- 将每个“++”都尝试换成“—”，看对手能不能赢，如果对手不能赢，则我们就赢了。