Introduction to Programming in Python, Aug-Dec 2014
                          Assignment 1
                  Due Sunday, 31 August, 2014

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Instructions:

1. For each question, write a separate Python program with the
   filename indicated in the question.

   Zip your solutions into a single archive (any name is OK for
   the zip file) and submit the zip file via moodle.

   If you don't name your files correctly, you risk losing marks.

2. If the question asks for a function, you *must* write a
   function in Python (i.e., def f(x): ... )  Ensure that the
   function you define has the name indicated in the question.

   If you add code to your file test your function, make sure to
   *remove* this code when you submit your solution.  The Python
   file you submit should have *only* the function definition.

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Problems

1. Filename: matched.py

   Write a Python function "matched(s)" that takes as input a
   string s and checks if the brackets "(" and ")" in s are
   matched: that is, every "(" has a matching ")" after it and
   every ")" has a matching "(" before it.  Your function should
   ignore all other symbols that appear in s.  Your function
   should return True if s has matched brackets and False if it
   does not.

   Here are some examples to show how your function should behave:

   >>> matched("zb%78")
   True
   >>> matched("(7)(a")
   False
   >>> matched("a)*(?")
   False
   >>> matched("((jkl)78(A)&l(8(dd(FJI:),):)?)")
   True


2. Filename: removeduplicates.py

   Write a Python function "removeduplicates(l)" that removes all
   duplicate values from l.  Your function should retain the
   first copy of each distinct value --- in other words, you
   should preserve the order in which values appear in l.

   Duplicates could be simple values such as numbers or complex
   values such as strings and lists.  You need to remove
   duplicates only at the top level of the list --- if a list
   contains another list as an element with duplicate values, the
   nested list can remain as it is.

   Your function should return a new list with duplicates
   removed.  It not modify the input list l.

   Here are some examples to show how your function should behave:

   >>> xlist = [7,2,5,7,2,9]
   >>> newxlist = removeduplicates(xlist)
   >>> xlist
   [7,2,5,7,2,9]
   >>> newxlist
   [7,2,5,9]

   >>> xlist = [7,2,"hello",2,[5,5],"hello",9,[5,5]]
   >>> newxlist = removeduplicates(xlist)
   >>> xlist
   [7,2,"hello",2,[5,5],"hello",9,[5,5]]
   >>> newxlist
   [7,2,"hello",[5,5],9]

3. Filename: splitwith.py

   Write a Python function "splitwith(l,x)" that uses x as a
   separator to split the list l into sublists.  Your function
   should return the list of sublists generated by splitting l in
   this way: all occurrences of x should be omitted.  In other
   words, if your function returns the list of lists
   [l1,l2,...,lk] then it should be the case that
  
         l == l1 + [x] + l2 + [x] + ... + [x] + lk

   - If there is no occurrence of x in l, the value returned
     should be list consisting of a single inner list which is
     the entire input list l.

   - If x occurs at the first/last position of the list, one of
     the sublists (before/after x, respectively) will be the
     empty list.

   Here are some examples to show how your function should behave:

   >>> splitwith([7,2,5,7,[2,7],9],7)
   [[],[2,5],[[2,7],9]]

   >>> splitwith([7,2,5,7,[2,7],9],8)
   [[7,2,5,7,[2,7],9]]

   >>> splitwith([7,2,[8],8,[8],[[8],7],2,9],[8])
   [[7,2],[8],[[[8],7],2,9]]


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