String s contains lowercase letters, digits, "(" and ")", satisfying the following rules: - Two digits cannot be adjacent. - Two "(" cannot be adjacent. - One "(" and one ")" cannot be adjacent. - After any digit, there must be "(". - The quantities of "(" and ")" are equal. Change string s until new string t created, t contains only lowercase letters. These are changing rules: - Sub-strings with form "n(p)", can change to "pp...p" (n times p), where n is a digit and p is a string. - If p still contains "(", ")" or digits, continue to implement the above changing method. Request: Implement function expand (string s); Where s is a string with the above form; return the result is a string containing only lowercase letters. Example: - String "2(ab3(cde)x)" changes into "abcdecdecdexabcdecdecdex". - String "2(x0 )3(z)" changes into "xxzzz". Note: In this exercise, libraries iostream, string and using namespace std; have been used. You can add other functions for your answer, but you are not allowed to add other libraries. For example: Result Test cout < < expand("2(ab3(cde)x)") < < " "; abcdecdecdexabcdecdecdex cout < < expand("2(x0(y))(z)") < < " "; xxzzz