Problem Statement  
The front of your house is covered with decorative square bricks, and you're worried that some of the bricks aren't properly supported and may fall down. You want to add enough bricks so that the wall is stable. In the below diagram, bricks are marked with 'X' and empty spaces are marked with '.'.
..X...X..... ....X.X...XX ...........X ..X.......X. The wall is stable if each brick is supported by bricks all the way to the ground. To fix the wall above, you would need to add 8 bricks in the positions marked with '#' below: ..X...X..... ..#.X.X...XX ..#.#.#...#X ..X.#.#...X# Each element of wallRows contains one row of the wall  in order from top to bottom  with 'X' for bricks and '.' for open spaces. Return the minimum number of bricks that must be added in order to make the wall stable (see example 0 for more info).  
Definition  
 
Constraints  
  wallRows will contain between 1 and 50 elements, inclusive.  
  Each element of wallRows will contain between 1 and 50 characters, inclusive.  
  Each element of wallRows will contain the same number of characters.  
  Each element of wallRows will contain only '.' and 'X' characters.  
Examples  
0)  
 
1)  
 
2)  
