Flip Game

/**
Flip Game
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 compute all possible states of the string after one valid move.
For example, given s = "++++", after one move, it may become one of the following states:
[
  "--++",
  "+--+",
  "++--"
]
If there is no valid move, return an empty list [].
*/

public class FlipGame{
public List<String> generatePossibleNextMoves(String s) {
List<String> res = new ArrayList<>();
for(int i=1; i<s.length(); i++){
if(s.charAt(i)=='+' && s.charAt(i-1)=='+'){
res.add(s.substring(0, i-1)+"--"+s.substring(i+1, s.length()));
}
}
return res;
}
}