224 C. Lab Assignments
C.6 Lab Assignment C.6
You are to implement a variation of the Jumble puzzle code that will recursively
generate legal variable names for Java.
You should create a class called RecursiveVariableName that will contain
the methods.
You are free to use wholesale any and all code from the sample code for the
Jumble puzzle.
The diļ¬erence between this and the Jumble puzzle is that not all variable
names, that is, all permutations of the input, are legal. Your program must
ļ¬lter out the strings generated that would begin with something other than
a letter. Further, by convention for this assignment, you should not allow a
variable name to end with yz (let us assume that you are working on a project
for which these variable names would be reserved for some other part of the
project.)
Note that there are two possible ways of doing this ļ¬ltering of permuta-
tions. You could wait until the entire permutation is generated and then do the
ļ¬ltering, or you could try to ļ¬lter out on the ļ¬y. In the case of symbols that
would start with a non-alpha character, this could be done easily. In the case
of symbols that end with yz it is more complicated because you would have to
detect in the middle of the permutation code that you had two letters left, y
and z, and that you could not choose the yļ¬rst.
In general, ļ¬ltering at the end means that you may have generated a number
of permutations that you throw away, which is wasteful of CPU time. If you
ļ¬lter as soon as possible, then you donāt go down the generation tree for all
the recursive calls that would follow a bad choice. You should probably check
at the beginning that your ļ¬rst character is alphabetic.
On the other hand, a complicated test in the middle of generating the
permutations isnāt a good idea unless you know there will be a large chunk of
the search tree that is carved away, and since the test for the invalidity of the
yz ending is to be done at the very bottom of the recursive tree, itās probably
just as easy to wait till the end and throw out the illegally-ending words when
you hit bottom.
You have several test symbol sets on the Moodle website. The small ones you
can do and examine by hand. The longer one will produce a very large number
of variable names, so you can perhaps only test on that input by counting the
number of legal strings and making sure that you get the correct count.
