Text Editor with Undo/Redo

Text Editor with Undo/Redo

Implement append/delete editing with full undo and redo — the Command pattern's home turf.

Requirements

• append and delete are edits; undo/redo navigate edit history; read inspects.
• A new edit clears the redo stack — after undoing twice and typing something new, the two undone edits are unreachable (exactly how every real editor behaves).
• undo/redo beyond the ends of history are silent no-ops.
• delete k with k larger than the document deletes everything (and is still one undoable edit).

API to implement

Implement the class TextEditor. The I/O driver is already written in the starter code — it parses the command script below and calls your methods. You only implement the class.

| Command | Returns | Behavior | |---|---|---| | append <text> | — | Append text (no spaces) to the document. Clears the redo history. | | delete <k> | — | Delete the last k characters (all of them if fewer exist). Implemented as the method remove (delete is a keyword in C++). Clears the redo history. | | undo | — | Revert the most recent un-undone edit. No-op if there is nothing to undo. Undone edits become redoable. | | redo | — | Re-apply the most recently undone edit. No-op if there is nothing to redo. | | read | string | Return the current document, or - if it is empty. |

Input format

The first line contains Q, the number of operations. Each of the next Q lines is one command as listed above. String arguments contain no spaces.

Output format

For each command with a non-void return, print its result on its own line, in order. The driver does this for you — your methods just return values.

This is a design problem: the hidden tests exercise edge cases and interaction sequences, not performance tricks. Model the state cleanly and the tests will pass.

11
append hello
append world
read
undo
read
redo
read
undo
undo
undo
read

helloworld
hello
helloworld
-

8
append abc
delete 2
read
undo
read
append z
redo
read

a
abc
abcz