Please Forward: Ruby Quiz Submission

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From: "btbeal" <btbeal@swbell.net>
Date: April 22, 2006 5:00:23 PM CDT
To: <submission@rubyquiz.com>
Subject: Please Forward: Ruby Quiz Submission

Hello,

This is my first submission to Ruby Quiz. I wrote up a little explanation
of how the program works, which you can use or not, as you wish. I didn't
include a data file to keep it short. Hopefully the tabs will expand again
when you copy the code into a text editor.

- Robert Beal (Austin, TX)

------------------------------------------------------------
Program Explanation (Quiz 76--Text Munging)

The heart of the program is the function "create_random_permutation".
It creates an array of the numbers 0...length and a second, empty array.
Then it deletes a number randomly from the first array and appends the number
to the second array. Afterwards, the second array is returned. The optional
arguments allow one to shift the range of numbers stored in the array, and to
shift the indices where the range is stored.

The second function, "permute_word", first copies its string argument
in order to have a target to copy the permuted letters to. Next the word
length is calculated; words of 3 letters or less won't change. Otherwise,
2 is subtracted from the word's length (to omit the first and last letters)
and a permutation is calculated in the range (1...length-1). The letters are
copied from the original to the copy using the permuted values as
subscripts into the target string. Finally, the copy is returned.

The last function, "munge", reads in a file, munges it, and writes the
results back out to another file. The file is read in as one giant string,
and two indexes into the string are created. Index #1 points at the first
letter of a word, and Index #2 points at the first letter past that word.
Each is moved forward in alternating turns until they bracket a word, the word
is munged in place, and the process repeats until both indexes wind up at the
end of the string.

-------------------------------------------------------------
The Program (Quiz 76--Text Munging)

# Return a permutation of the values (0...length) in an array.
# If "offset" is given, return [offset,...,length+offset].
# If "pad" is given, return [nil,...,nil, <rest of perm>].
# If offset == pad, you can index into the array with the
# same set of values that you get out of it.
def create_random_permutation(length, offset=0, pad=offset)
a = Array.new(length) {|i| i + offset}
b = Array.new(pad, nil)
(length - 1).downto(0) {|i| b.push(a.delete_at(rand(i + 1)))}
b
end
alias crp create_random_permutation

# Given a string, permute the characters in the interior of (a copy of) the string
# (i.e. leave the first and last characters alone) and return the result.
def permute_word(word)
word2 = word.clone
if word.length > 3
  p = crp(word.length - 2, 1)
  1.upto(word.length - 2) {|i| word2[p[i]] = word[i]}
end
word2
end

# The main program.
# Read a text file, munge all words, and write out the result.
# "Munging" means to permute all the interior letters of a word.
# The first and last letters in the word and all other characters
# (punctuation, blanks, etc.) in the string are left where they are.
# A simple filename (no path, no extension) is the argument;
# the file is assumed to be in the current directory, the input
# extension is .txt, and the output extension is .out.
def munge(name)
infile = name + ".txt"
outfile = name + ".out"
line = File.open(infile) {|f| f.read}
#i1 points at the first character in a word.
#i2 points at the first character after a word.
i1 = i2 = 0;
while i1 < line.length || i2 < line.length
  i2 += 1 while i2 < line.length && line[i2, 1] =~ /[[:alpha:]]/ #in a word
  line[i1...i2] = permute_word(line[i1...i2])
  i1 = i2
  i1 += 1 while i1 < line.length && line[i1, 1] !~ /[[:alpha:]]/ #not in a word
  i2 = i1
end
File.open(outfile, "w") {|f| f.write(line)}
# line
end

---------------end--------------------------------

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