3612. Process String with Special Operations I

You are given a string s consisting of lowercase English letters and the special characters: *, #, and %.

Build a new string result by processing s according to the following rules from left to right:

• If the letter is a lowercase English letter append it to result.
• A '*' removes the last character from result, if it exists.
• A '#' duplicates the current result and appends it to itself.
• A '%' reverses the current result.

Return the final string result after processing all characters in s.

class Solution {
public:
    string processStr(string s) {
        string res = "";
        for(auto& ch : s) {
            if(isalpha(ch)) res.push_back(ch);
            else if(ch == '*') {
                if(res.size()) res.pop_back();
            } else if(ch == '#') res = res + res;
            else if(ch == '%') {
                reverse(begin(res), end(res));
            }
        }
        return res;
    }
};©leetcode