With a typical operating system, a filesystem consists of a number of directories, in which reside files. These files generally have a canonical
location, known as the absolute path (such as /usr/games/bin/kobodl), which can be used to refer to the file no matter where the user is on a
system.
Most operating system environments allow you to refer to files in other directories without having to be so explicit about their locations, however.
This is often stored in a variable called PATH, and is an ordered list of locations (always absolute paths in this problem) to search for a given name.
We will call these search paths.
In the brand-new crash shell, paths are handled somewhat differently. Users still provide an ordered list of locations that they wish to search for files
(their search paths); when a particular filename is requested, however, crash tries to be even more helpful than usual. The process it follows is as
follows:
If there is an exact match for the filename, it is returned. Exact matches in locations earlier in the list are preferred. (There are no duplicate
filenames in a single location.)
If there are no exact matches, a filename that has a single extra character is returned. That character may be at any point in the filename, but
the order of the non-extra characters must be identical to the requested filename. As before, matches in locations earlier in the list are
preferred; if there are multiple matches in the highest-ranked location, all such matches in that location are returned.
If there are no exact matches or one-extra-character matches, files that have two extra characters are looked for. The same rules of precedence
and multiple matches apply as for the one-extra-character case.
If no files meet the three criteria above, no filenames are returned. Two characters is considered the limit of "permissiveness" for the crash
shell.
So, for example, given the two files bang and tang, they are both one character away from the filename ang and two from ag. (All characters in this
problem will be lowercase.) In the sample data below, both cat and rat are one character away from at.
Given a complete list of locations and files in those locations on a system, a set of users each with their own ordered lists of search paths, and a set of
files that they wish to search for, what filenames would crash return?
For the purposes of simplification, all locations will be described by a single alphabetic string, as will filenames and usernames. Real operating
system paths often have many components separated by characters such as slashes, but this problem does not. Also note that users may accidentally
refer to nonexistent locations in their search paths; these (obviously) contain no files.