FlipGame293.java

/**
 * 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.
 * 
 * Example:
 * Input: s = "++++"
 * Output: 
 * [
 *   "--++",
 *   "+--+",
 *   "++--"
 * ]
 * Note: If there is no valid move, return an empty list [].
 */

public class FlipGame293 {
    public List<String> generatePossibleNextMoves(String s) {
        List<String> res = new ArrayList<>();
        if (s == null || s.length() <= 1) return res;
        char[] chars = s.toCharArray();
        
        for (int i=0; i<s.length()-1; i++) {
            if (chars[i] == chars[i+1] && chars[i] == '+') {
                chars[i] = '-';
                chars[i+1] = '-';
                res.add(new String(chars));
                chars[i] = '+';
                chars[i+1] = '+';
            }
        }
        
        return res;
    }

}