294. Flip Game II

You are playing a Flip Game with your friend.

You are given a string currentState that contains only '+' 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.

Return true if the starting player can guarantee a win, and false otherwise.

 

Example 1:

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

Example 2:

Input: currentState = "+"
Output: false

 

Constraints:

• 1 <= currentState.length <= 60
• currentState[i] is either '+' or '-'.
• There cannot be more than 20 consecutive '+'.

 

Follow up: Derive your algorithm's runtime complexity.