C++

include

include

include

include

include

include

using namespace std;

static stack sString{}; void append(string &s,string appStr){ sString.push(s); s=s+appStr; //cout<<"Appended: "<

void del( int k, string &s){ sString.push(s); if(s.size()-k >=0) s.erase(s.size()-k,k); //cout<<"Deleted: "<

void print(int k,const string &s){ cout << s[k-1]<

void undo(string &s){

s=sString.top();
sString.pop();
//cout<<"After Undo: "<<s<<endl;

}

vector splitString(string s,string delimiter) { vector out{}; int start=0; int end=s.find(delimiter,start); while(end!=string::npos) { out.push_back(s.substr(start,end-start)); start=end+delimiter.length(); end=s.find(delimiter,start); } out.push_back(s.substr(start)); return out; }

int main() { /* Enter your code here. Read input from STDIN. Print output to STDOUT */
int q; cin>>q; string out{}; while (q>=0) { string s; getline(cin,s); vector split = splitString(s, " ");

    if(split[0]=="1")
    {
        append(out, split[1]);
    }
    else if(split[0]=="2")
    {
        del(stoi(split[1]), out);
    }
    else if(split[0]=="3")
    {
        print(stoi(split[1]), out);
    }
    else if(split[0]=="4")
    {
        undo(out);
    }
    q--;
}    
return 0;

}