如何在二维数组中留下某种标记，该标记会告诉程序在该位置执行某些操作

Question

I am working on a little game that uses two-dimensional array for a board we play on. I implemented Undo method that will go back in history step by step with every Button click. The thing is in some cases the Undo method must do something else in a special situation and it might happen many times during the game.

I know the one way would be to store 'x' and 'y' (which are responsible for position on the board) when I reach the place where it will be needed to do something else if we come back here later. Then add if in Undo Action Listener that if position we come back to .equals any of stored x and y then do the thing. But it is quite not efficient I would say and I am wondering if there is a way to leave a mark that will tell the program that when I come back here the Boolean I created will .equal true and do the thing.

Here is the overview of the board:

Answer 1

I don't understand why an if statement will be inefficient. I will add constant time (if only your equals method has constant time) to your undo operation, so the big-o time of your operation will not be modified.

However, if you prefer another way to do that, then you could save an object in each cell. That object should have a boolean property that you will check when doing the undo operation.

I would prefer using an if statement, but is up to you.

Answer 2

You are using a 2-dimensional array - an array of what? Considering you have letters in your picture I presume something like String[][].

However you can also do an array of your own class. Something like a class "Cell". Give this class two members - firstly the payload (aka the data you currently have) and secondly a boolean as your mark.

Answer 3

Separate concerns. The board shouldn't have to also store its history. Keep a journal of actions and have a way to play them back in reverse.

This is exactly how relational databases cater for rollbacks; they keep a log of every change and can undo everything in it. The log is usually a before snapshot of the state of the data being changed. One simple way you could implement it in your case would be to store a snapshot of every board and undo would simply swap historic boards in for the current board.

This might seem “heavy”, but it's the way massive high transaction rate databases do it, and it's way simpler to implement and bulletproof, because you don't need to know how to undo a specific action. Further, it means boards need to know less, in fact they don't even need to know they can be undone.