TopCoder problem "Filter" used in SRM 89 (Division II Level Three)

Problem Statement

A 2-dimensional digital picture has been received from a satellite as a String[]. The characters in each String are only '0' or '1' (zero or one). Some of the '1's are noise that should be filtered out. The filtering rule is that a '1' should be removed if it is not part of a cross pattern consisting of 5 '1's in the following configuration:

     1
    111
     1

Write a class Filter that contains the method removable that takes a String[], picture, and returns the number of '1's that should be filtered out of picture.

Definition

Class:	Filter
Method:	removable
Parameters:	String[]
Returns:	int
Method signature:	int removable(String[] picture)
(be sure your method is public)

Notes

Cross patterns may overlap. (See example 2)

Constraints

picture contains between 1 and 50 elements, inclusive.

each String in picture contains between 1 and 50 characters, inclusive.

each String in picture has the same length.

each String in picture contains only the characters '0' and '1' (zero and one).

Examples

{"00110",
 "00110",
 "00110"}

Returns: 6

There are no cross patterns. All the '1's can be removed.

{"00110",
 "00111",
 "00110"}

Returns: 2

There is one cross pattern. 2 of the '1's can be removed.

{"00111",
 "01111",
 "00110"}

Returns: 1

There are two (overlapping) cross patterns. Only the 1 in the upper right corner is not in some cross.