Step 1: Construct patterns that have exactly two solid characters in them and separated by no more than D spaces or "." characters. This is done by scanning the string s from left to right. Further, for each location we store start and end position of the pattern. For example, if s = abzdabyxd and K = 2, D = 2, then all the patterns generated at this step are: ab, a.z, a..d, bz, b.d, b..a, zd, z.a, z..b, da, d.b, d..y, a.y, a..x, by, b.x, b..d, yx, y.d, xd, each with its occurrence list. Thus ab = {(1, 2), (5, 6)}, a.z = {(1, 3)} and so on.