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 [].

class Solution {
public:
    vector<string> generatePossibleNextMoves(string s) {
        vector<string> result;
        if (s.size() < 2) return result;
        
        for (int i = 1; i < s.size(); i++) {
            if (s[i] == '+' && s[i - 1] == '+') {
                s[i] = s[i - 1] = '-';
                result.push_back(s);
                s[i] = s[i - 1] = '+';
            } 
        }
        return result;
    }
};