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 <= 60currentState[i]is either'+'or'-'.
Follow up: Derive your algorithm's runtime complexity.