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I want to implement UNDO and REDO option(as we see in MS word etc). Can you suggest me a data structure for it, and how can i implement it.?
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If “UNDO” string is encountered, pop the top element from Undo stack and push it to Redo stack. If “REDO” string is encountered, pop the top element of Redo stack and push it into the Undo stack. If “READ” string is encountered, print all the elements of the Undo stack in reverse order.
Application of Doubly Linked Lists: Redo and undo functionality. Use of Back and forward button in a browser.
The standard is to keep the Command objects in a stack to support multi level undo. In order to support redo, a second stack keeps all the commands you've Undone. So when you pop the undo stack to undo a command, you push the same command you popped into the redo stack.
The best way to look at undo/redo is two stacks of operations the user has performed: The Undo stack is the "history" of what they've done. The redo stack is the breadcrumbs back to the initial state before they started undoing.
It isn't a data structure but a design pattern. You're looking for the Command Pattern.
The standard is to keep the Command objects in a stack to support multi level undo. In order to support redo, a second stack keeps all the commands you've Undone. So when you pop the undo stack to undo a command, you push the same command you popped into the redo stack. You do the same thing in reverse when you redo a command. You pop the redo stack and push the popped command back into the undo stack.
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Actually, the standard pattern for this functionality (Gang of Four, even) is Memento.
Also, while most programs use Undo/Redo stacks, afficionados of certain text editors prefer Undo/Redo trees so that they don't lose their entire history if they undo a few commands, try a new one, and change their minds.
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