You are playing a Flip Game with a friend.

You are given a string currentState consisting only of the characters '+' and '-'. Players take turns flipping two consecutive "++" into "--". The game ends when a player cannot make a move, at which point the other player wins.

Return all possible states of currentState after performing exactly one valid move. The answer may be returned in any order. If no valid move exists, return an empty list.

Constraints:

• $1 \leq$ currentState.length $\leq 500$

• currentState[i] is either '+' or '-'

Now, let's take a moment to make sure you've correctly understood the problem. The quiz below helps you check if you're solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.