Score : 300 points
You are given a grid of squares with H horizontal rows and W vertical columns, where each square is painted white or black.
HW characters from A_{11} to A_{HW} represent the colors of the squares.
A_{ij} is #
if the square at the i-th row from the top and the j-th column from the left is black, and A_{ij} is .
if that square is white.
We will repeatedly perform the following operation until all the squares are black:
Find the number of operations that will be performed. The initial grid has at least one black square.
#
or .
.Input is given from Standard Input in the following format:
H W A_{11}A_{12}...A_{1W} : A_{H1}A_{H2}...A_{HW}
Print the number of operations that will be performed.
3 3 ... .#. ...
2
After one operation, all but the corners of the grid will be black. After one more operation, all the squares will be black.
6 6 ..#..# ...... #..#.. ...... .#.... ....#.
3