Sometimes, when listing files in a filesystem, it is desirable to view the files in a tree-like format. This can provide a visual representation of which files reside in which directories.
We first define how filenames with their full paths will be given. Each filename will consist of a leading slash ('/'), followed by a sequence of names separated by slashes. The names shall consist of one or more lower case letters. The name after the last slash identifies the file, and all the other names identify the directories and subdirectories that the file is in. For example, the path "/usr/bin/bash" is the full path name of the file "bash" in the directory "bin", which is a subdirectory of "usr". "usr" resides in the root directory "/".
Next, we define how the filenames should be displayed in the tree. For each directory that has subdirectories or files, sort all the subdirectory and file names in alphabetical order, and branch them underneath the containing directory's name. A branch is accomplished by placing a plus symbol ('+') in the column under the first letter of the containing directory's name (use preceding spaces to place the plus character in the correct column). Then place a dash character ('-') after the plus symbol. Finally, place the name of the subdirectory or file after the dash. If that name is a subdirectory which has its own elements, perform the same branching steps for that subdirectory before doing the next element of the containing directory. Finally, if two elements of a directory are not on adjacent lines in the output, connect their '+' symbols by putting vertical bars ('|') in the same column as the '+' symbols for all the lines in between the two elements. One special case, the root directory will be output as "ROOT", and will always be the first line in the output. To visually see the result of this method, look at the examples.
Given a String files, which contains full path file names, return a String with the file and directory names displayed in a tree format as defined above.