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How to detect if a file has changed?

Since this is a word processor program, it can have a history of actions as well. You can maintain 2 stack, one for historical actions (changes that have already been incorporated), and another for future actions (changes that had been applied, but now have been reverted in a linear fashion).

For example, every character typed in sequence can be one item in the actions stack, and delting it back could be equivalent to popping that action from stack of history items to stack of future actions (In case you need to redo the actions).

Now, whenever the history actions' stack is not empty, you prompt the user to close the file on closure.

For sake of simplicity, you can have limited number of history items (say last 100 actions). Then, since each add/subtract to document is happening with every user action, there is hardly any delay, and figuring out whether the stack is empty or not is an O(1) operation.

Categories : Algorithm

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