You are playing the following Flip Game with your friend: Given a string that contains only these two characters:
-, you and your friend take turns to flip two consecutive
"--". 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.
For example, given
s = "++++", return true. The starting player can guarantee a win by flipping the middle
"++" to become
Derive your algorithm's runtime complexity.