293. Flip Game

Question:

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 [].

Solution:(String)

From i=0 to i=n-2, if there exists two consecutive "++", then it will be one result.
O(n).

Code(C++):

class Solution {
public:
    vector<string> generatePossibleNextMoves(string s) {
        int n = s.size();
        int i = 0;
        vector<string> res;
        while(i<n-1){
            if(s[i]=='+' && s[i+1]=='+'){
                string tmp = s;
                tmp[i] = '-';
                tmp[i+1] = '-';
                res.push_back(tmp);
            }
            i++;
        }
        return res;
    }
};