Project 7: Huffman Code

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Project 7 Huffman Code
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Project 7 Huffman Code

• Extend the most recent version of the Huffman
  Code program to include decode information in the
  binary output file and use that information to
  restore the original ASCII text.

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Embedding the Code

• In order for the coded file to be useful, we have
  to store the code along with it.
• Then we can read and decode the file at a later
  time.
• Even on a different computer (with the same
  architecture)
• In order to decode
• First read the code
• Then read and decode the message

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Serialization

• We will need to serialize the decode tree.
• Convert data structure into a byte array.
• Necessary any time an object is to be written to
  a file or transmitted over a network.
• Also deserialize.
• Convert byte array back into the data structure
  in memory.
• Serialize and deserialize methods are required
  for any class whose objects need to be preserved
  in files or transmitted over a network.

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Serialization

• We will write the serialized decode tree into the
  binary output file ahead of the coded message.
• On decode, first read back and deserialize the
  decode tree, then read and decode the message.
• Serialization and deserialization are byte level
  operations.
• Don't want to do one bit at a time.
• Will need new operations in our binary file
  classes.
• http//www.cse.usf.edu/turnerr/Data_Structures/Do
  wnloads/Project_7_Binary_File_Classes/

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Serializing the Decode Tree

• How do we convert the decode tree into a byte
  array that can be converted back into a decode
  tree elsewhere?
• Don't output pointers!
• We can't put nodes back into the same memory
  locations.
• Have to create new nodes and link them together
  in the same way they were linked in the original
• but at new memory locations.
• Applies to all serialization operations.

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How to serialize a decode tree?
Note that each nonleaf node has two child nodes.
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How to deserialize a decode tree?

• Need the child node addresses in order to restore
  a nonleaf node.
• Get restored left child address.
• Get restored right child address.
• Get data for node.
• Create new node with data, and pointers to left
  child and right child.

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How to deserialize a decode tree?

• Work from the bottom up.
• Leaf nodes can be restored immediately from the
  serialized data.
• Push addresses onto a stack.
• Get parent data from serialized data.
• Pop left child address.
• Pop right child address.
• Restore parent node.
• Push parent node address onto stack.

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Serialization Algorithm

• Do a postorder depth-first traversal
• Output node data as each node is visited.

• Output only the node data
• not the pointers.

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Deserialization Algorithm

• While any node data left in serialized stream
• Get next node data from serialized stream.
• If it is a leaf
• Create a new node in memory with the data.
• Push address of new node onto stack.
• Else
• Pop child address from stack.
• Pop child address from stack.
• Create new node in memory with data from the
  serialized stream and child addresses from the
  stack.
• Push address of new node onto the stack.

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Implementing Serialization

• Add code to class Huffman_Tree to serialize and
  deserialize the decode tree.
• Output and input data from the Char_Freq objects.
• Need serialize and deserialize methods in that
  class also.

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Implementing Serialization

• How do we indicate end of the serialized decode
  tree?
• Use a sentinel.
• A unique value that cannot appear as real data.
• Char_Freq(0, 0)

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Sample Run
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Test on Full Text
Delete screen output of decoded text.
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The Files
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Development Environment

• You may develop your program on any system you
  like.
• The same source files should compile and run on
  either Windows or Linux.

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Ground Rules

• You may work with one other person.
• OK to work alone if you prefer.
• If you do work as a pair
• Work together!
• Both members are expected to contribute.
• Both members should understand the program in
  detail.
• Submit a single program.
• Do not share your code with other students.
• Before or after submitting the project.
• OK to discuss the project.
• Do not copy any other students work.
• Dont look at anyone elses program.
• Dont let anyone look at your program.

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Ground Rules

• Except for code posted on the current class web
  site
• Do not copy code from the Internet
• or any other source.
• Write your own code.

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Submission

• Project is due by 1159 PM, Sunday night, April
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• Deliverables
• Source files only.
• Zip using Windows "Send to Compressed Folder"
• If you work with another student, include both
  names in the assignment comments.
• Other student submit just a Blackboard submission
  comment including both names.
• End of Presentation

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