Detect unjoined area algorithm

[Zekallinos]

I need to detect if two coordinates in the map are joined (or two areas, same thing), meaning if there is a possible path from Point A to Point B. Any obstacle (event, impassable tile, etc) can prevent the existence of such a path (if the map is pretty cluttered).

The obvious thing to do first is make a sort of array that contains empty tiles and "walls".

But then what? How would I make a efficient algorithm that knows if there is a possible path (I don't need to find the actual path)?. Brute force is more or less an option. Suggestions or references?

 

[Zekallinos]

Though about it more. I could preprocess the map to separate the biggest into nodes, add connections between nodes for every (narrow) path. Then whenever something passes by one of these narrow paths, I could check the immediate surroundings to check if that thing (event or whatever) blocks that path. So I could remove that connection between the two area (nodes). It's much easier to check if two nodes are not connected then two areas.

Still, it's quite error-prone (how do I know if my big area isn't split?). There must be some other way right?

 

[silver wind]

You can put an edge between each tile and any of the 4 tiles next to it(left,right,up,down) which isn't blocked. Next it's just implementing one of the famous shortest-path algorithms.
If no path is found, the areas are unjoined.