Given an area represented as a bitmap, identify the minimum mobile sensors required to cover the occupied area to collect information. “1” represents occupation
& “0” represent unoccupied area. The sensor can be placed on occupied area as well as the unoccupied one.

Sample input-1:

0 0 0 0
0 1 1 0
0 1 1 1
0 1 0 0

A sensor can cover; (itself, region above, below, right and left).

  1
1 1 1
  1

Find minimum sensors needed to cover the whole occupied region and also the positions where it got to be placed;
In the above example, we need two sensors to cover all the region; at (2, 1) and (2, 2).
Can someone please suggest the thinking process for this kind of problems? and any relavant examples and point any similar problems.