How to create an adjacency matrix based on a 2D map?

Question

Algorithms

Hello. The problem is the following, there is a map (as in the picture). You need to build an adjacency matrix, where 1 row is the cell where the monster is. What algorithm can do this?

Answer 1

Since there are no "portals", any cell can be accessed from a maximum of 4 adjacent ones.
Number the cells, go around each, count how many of the four neighbors are available - not a wall, not outside the map.