1047

class Solution {
public:
    string removeDuplicates(string s) {
        int i = 0, n = s.length();
        for (int j = 0; j < n; ++j, ++i) {
            s[i] = s[j];
            if (i > 0 && s[i - 1] == s[i]) // count = 2
                i -= 2;
        }
        return s.substr(0, i);
    }
};