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.

Example:

Input: s = "++++"
Output: 
[
  "--++",
  "+--+",
  "++--"
]

Note:

If there is no valid move, return an empty list[].

比较直接

class Solution {
    public List<String> generatePossibleNextMoves(String s) {
        List<String> res = new ArrayList<String>();
        if(s == null || s.length() < 2)
            return res;

        for(int i = 0; i < s.length() - 1; i++) {
            char c1 = s.charAt(i);
            char c2 = s.charAt(i + 1);

            if(c1 == c2 && c1 == '+') {
                StringBuilder str = new StringBuilder(s);
                str.setCharAt(i, '-');
                str.setCharAt(i + 1, '-');
                res.add(str.toString());
            }
        }

        return res;
    }
}