1957. Delete Characters to Make Fancy String

class Solution {
public:
    string makeFancyString(string s) {
        stack<char>st;
        for(int i = 0;i<s.length();i++){
            st.push(s[i]);
            if(st.size()>=3){
                char first = st.top();
                st.pop();
                char second = st.top();
                st.pop();
                char third = st.top();
                st.pop();
                if(first == second && second == third){
                    
                    st.push(second);
                    st.push(first);
                }else{
                    
                    st.push(third);
                    st.push(second);
                    st.push(first);
                }
            }
        }

        string ans = "";
        while(!st.empty()){
            ans += st.top();
            st.pop();

        }
        reverse(ans.begin(),ans.end());
        return ans;
    }
};