Apply Special String Commands

# Apply Special String Commands You are given a string `s` containing lowercase English letters and the commands `*`, `#`, and `%`. Start with empty working text and process `s` from left to right: - A lowercase letter appends that letter to the working text. - `*` removes the last character if the working text is nonempty. Otherwise it does nothing. - `#` appends a copy of the entire current working text to itself. - `%` reverses the current working text. Return the complete final text after all input characters have been processed. ### C++ Interface ```cpp class Solution { public: string processStr(string s); }; ``` ### Examples **Example 1** ```text s = "pq#%*r" Output: "qpqr" ``` The working text changes as follows: `"p"`, `"pq"`, `"pqpq"`, `"qpqp"`, `"qpq"`, `"qpqr"`. **Example 2** ```text s = "**t*#%" Output: "" ``` The first two removals do nothing. Appending `t` and removing it leaves empty text; copying and reversing that empty text keep it empty. ### Constraints - `1 <= s.length <= 20`. - Every character is a lowercase English letter or one of `*`, `#`, `%`. ### Clarifying Questions - Does `#` copy the input processed so far? No. It copies the current working text, including all earlier command effects. - Can `*` remove a command symbol from the input? No. It removes only the current working text's last character, if one exists. - Does `%` change the order of the remaining input commands? No. It affects only the text built so far. - Can the returned string be empty? Yes. ### What a Strong Answer Covers - The exact left-to-right meaning of all four kinds of input characters. - Correct behavior of removal, copying, and reversal on empty text. - Preservation of repeated letters and the order produced by earlier commands. - Time and memory bounds that account for repeated duplication, with at most twenty input characters. ### Follow-up Questions - Which of the three commands leave empty working text unchanged? - What happens when two reversal commands occur consecutively without another operation between them? ```hint Follow the commands Maintain the current text explicitly. Check whether it is empty before removing its last character, and duplicate a snapshot of the whole current text when processing #. ```