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 [].

Solution

public class Solution {
     public List<String> generatePossibleNextMoves(String s) {
        List<String> result = new ArrayList<>();
        if (s == null || s.length() <= 1) return result;

        for (int i = 0; i < s.length() - 1; i++) {
            if (s.charAt(i) == '+' && s.charAt(i+1) == '+') {
                StringBuffer sb = new StringBuffer(s);
                sb.replace(i, i + 2, "--");
                result.add(sb.toString());
            }
        }

        return result;
    }

}