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 twoconsecutive `"++"`

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

`[]`

.**Understand the problem:**

The problem only asks for flipping "++" into "--", NOT -- to ++. So the solution is to move all consecutive "++" into "--".

**Code (Java):**

public class Solution { public List<String> generatePossibleNextMoves(String s) { List<String> result = new ArrayList<>(); if (s == null || s.length() < 2) { return result; } for (int i = 0; i < s.length() - 1; i++) { if (s.charAt(i) == '+' && s.charAt(i + 1) == '+') { String s1 = s.substring(0, i); String s2 = "--"; String s3 = s.substring(i + 2); String temp = s1 + s2 + s3; result.add(temp); } } return result; } }

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