@Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + x;
        result = prime * result + y;
        return result;
    }
http://www.geeksforgeeks.org/divide-and-conquer-set-6-tiling-problem/
Test cases
Size of matrix is at least 2 and power of 2 always
Missing point could be on edges
Missing point could be in any of 4 quadrants
src/com/interview/multiarray/TilingProblem.java