include

include

include

include

include

include

using namespace std;

int main() { string S1 = ""; int Queries = 0; cin >> Queries; int Operations = 0; string S2 = ""; stack Temp; while (Queries--) { cin >> Operations; if (Operations == 1) { Temp.push(S1); cin >> S2; S1 += S2; } else if (Operations == 2) { Temp.push(S1); cin >> Operations; S1.erase(S1.size() - Operations, S1.size()); } else if (Operations == 3) { cin >> Operations; cout << S1[Operations-1] << endl;; } else if (Operations == 4) { S1 = Temp.top(); Temp.pop(); } } }

For Java 7. Ok. You need to know that i generated this by chatGPT, tell him to optimize my oringinal. Eventhrough it's still not good enough, but try a few times then it might pass.

import java.util.Scanner; import java.util.Stack;

public class SolutionSolution { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); int q = scanner.nextInt(); scanner.nextLine();

    StringBuilder currentText = new StringBuilder();
    Stack<Operation> history = new Stack<>();

    for (int i = 0; i < q; i++) {
        int type = scanner.nextInt();

        switch (type) {
            case 1: // Append
                String w = scanner.next();
                history.push(new Operation(1, w.length()));
                currentText.append(w);
                break;

            case 2: // Delete
                int k = scanner.nextInt();
                String deletedText = currentText.substring(currentText.length() - k);
                history.push(new Operation(2, deletedText));
                currentText.delete(currentText.length() - k, currentText.length());
                break;

            case 3: // Print
                int pos = scanner.nextInt();
                System.out.println(currentText.charAt(pos - 1));
                break;

            case 4: // Undo
                if (!history.isEmpty()) {
                    Operation lastOperation = history.pop();
                    if (lastOperation.type == 1) {
                        // Undo append: remove the last 'length' characters
                        currentText.delete(currentText.length() - lastOperation.length, currentText.length());
                    } else if (lastOperation.type == 2) {
                        // Undo delete: append the deleted string
                        currentText.append(lastOperation.data);
                    }
                }
                break;

            default:
                break;
        }
    }

    scanner.close();
}

static class Operation { int type; // 1 for append, 2 for delete int length; String data;

    Operation(int type, int length) {
        this.type = type;
        this.length = length;
    }

    Operation(int type, String data) {
        this.type = type;
        this.data = data;
    }
}

}

Simple cpp solution:

#include <iostream>
#include <algorithm>
#include<bits/stdc++.h>
using namespace std;

void append(string &s, string &w){
    s.append(w);
}

void deleteS(string &s, int k){
    if(s.length() == k)
        s.erase(s.begin(),s.end());
    else{
       k = s.length()-k;
       s = s.substr(0,k); 
    }    
}

void printK(string &s, int k){
    string :: iterator it;
    it = s.begin();
    advance(it,k-1);
    cout<<*it<<endl;
}

void undo(stack<string> &st, string &s){
    if(st.size() == 1){
        s = st.top();
        return;
    }
    if(!st.empty()){
        s = st.top();
        st.pop();
    }
}

int main() {
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */  
    int q;
    stack<string> st;
    string s;
    cin>>q;
    while(q--){
        int x;
        string w;
        cin>>x;
        if(x==1){
            cin>>w;
            st.push(s);
            append(s,w);                        
        }
        if(x==2){
            int y;
            cin>>y;
            st.push(s);
            deleteS(s,y);            
        }
        if(x==3){
            int y;
            cin>>y;            
            printK(s,y);
        }
        if(x==4){
            undo(st,s);
        }
    } 
    return 0;
}

JavaScript (NodeJS) Solution

let result = "";
const history = [""];

function processCommand(input) {
    const [command, option] = input.split(" ");
    switch (command) {
        case "1":
            result += option;
            history.push(result);
            break;
        case "2":
            result = result.slice(0, result.length - option);
            history.push(result);
            break;
        case "3":
            console.log(result[option - 1]);
            break;
        case "4":
            history.pop();
            result = history.at(-1);
            break;
        default:
            break;
    }
}

function processData(input) {
    input.split(/\r?\n/).slice(1).forEach(processCommand);
}