Flip Game -- LeetCode

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> res;
        for (int i = 0, n = s.size() - 1; i < n; i++)
            if (s[i] == '+' && s[i + 1] == '+') {
                string temp = s;
                temp[i] = temp[i + 1] = '-';
                res.push_back(temp);
            }
        return res;
    }
};