CS 261 Fall 2006

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CS 261 - Fall 2006

• Intro to ADT Bag

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What is a Bag?

• A simple collection, allowing add, removal, and
  searching
• Add (newElement)
• Contains (testElement)
• Remove (testElement)
• Size ()
• Iterator () / more on this on Friday /

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Adding is easy

• Add is an easy operation
• Since we dont care where it is added (unlike
  stack or queue), we can simply use whatever code
  we have previously defined
• That is, we have already solved this problem

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Contains test

• Testing to see if an element is contained is also
  pretty easy
• Simply loop over the collection, testing each
  element.
• What is the complexity of this operation?
• (Later, we will see better solutions)

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What does equality mean?

• Just as we used EleType to represent an unknown
  element type - we need a general way to represent
  testing equality.
• ifndef EQ
• define EQ(a, b) (a b)
• endif

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What does a loop look like?

• What does a loop look like for a dynamic array?
• What does a loop look like for a linked list?
  (in part, depends upon whether we have sentinels
  or not)

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Dynamic Array Loop

• dyArray d
• Int i
• For (i 0 i lt d-gtsize i)
• if (EQ(testElement, d-gtdatai))

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What does a list loop look like?

• Struct list lst
• Struct dlink lnk
• For (lnk lst-gtfirstLink
• lnk ! lst-gtSentinel lnk lnk-gtnext)
• if (EQ(testElement, lnk-gtvalue))

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Remove

• Remove requires removing elements from middle of
  collection
• For dynamic array, need to move values down
• For linked list, need to remove link

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Dynamic Array Remove
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Remove

• Need to write a loop to move elements down.
• What is the complexity of this operation?

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Linked List Remove

• Already solved this problem - wrote removeLink
• What is the complexity of removing the link?
• What is the complexity of finding the element you
  want to remove?

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Your turn

• Questions?
• Complete worksheets that show how to make a bag
  out of a dynamic array
• And how to make a bag out of a linked list.