Flip Game

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