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Build Huffman Tree with Priority Queue in C

Posted on 2007-04-08
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Last Modified: 2011-09-20
Hi,

I am working on the Huffman Algorithm in C for my class project.  I am having trouble building the huffman tree to start.  This is what I have so far:

TreeNode * buildHuffmanTree(int freqs[256])
{
  int i;
  PriorityQueue forest;
  TreeNode* leftP, *rightP, *tmp;
  TreeEntry* top;
 
  CreatePQueue(&forest);
 
  /* YOU FILL IN THE REST OF THIS CODE */
  for (i = 0; i < 256; i++)
  {
      if (freqs[i] > 0)
        {
          leftP = malloc (sizeof(TreeNode));
          leftP->left = NULL;
          leftP->right = NULL;
          pqInsert(leftP, &forest);
      }
   }

        while (freqs[i] > 1)
      {
         
          leftP = deleteMin(&forest);
          rightP = deleteMin(&forest);
          tmp->left = leftP;
          tmp->right = rightP;
          tmp = MakeNode(top->symbol, top->weight, tmp->left, tmp->right);
          pqInsert(tmp, &forest);
      }
      return tmp;
{

If anyone has any advice I would appreciate it.  Thanks.
0
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Question by:Karamelg11
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8 Comments
 

Author Comment

by:Karamelg11
ID: 18873454
I am familiar with all those web pages, and it doesn't really help me with implementing the actual code to create a tree using a priority queue.
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LVL 84

Expert Comment

by:ozo
ID: 18873511
are you able to implement deleteMin and pqInsert?
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LVL 84

Expert Comment

by:ozo
ID: 18873515
0
 
LVL 16

Expert Comment

by:AlexNek
ID: 18873521
What is then your troubles? If you know algorithm very well then try to write pseudo code and then convert it to C
Here is one sample
http://www.codeproject.com/cpp/Huffman_coding.asp
0
 

Author Comment

by:Karamelg11
ID: 18873596
ozo - I am able to implement deleteMin and pqInsert and  I have in the following code.  AlexNek, converting it to C is where I am having the problem.  I had posted the code I had written in hopes of getting criticism on what I may be doing wrong.


TreeNode * buildHuffmanTree(int freqs[256])
{
  int i;
  PriorityQueue forest;
  TreeNode* leftP, *rightP, *tmp;
  TreeEntry* top;
 
  CreatePQueue(&forest);
 
  /* YOU FILL IN THE REST OF THIS CODE */
  for (i = 0; i < 256; i++)
  {
      if (freqs[i] > 0)
        {
          leftP = malloc (sizeof(TreeNode));
          leftP->left = NULL;
          leftP->right = NULL;
          top->weight = freqs[i];
          top->symbol = (char) i;
          leftP = MakeNode(top->symbol, top->weight, leftP->left, leftP->right);
          pqInsert(leftP, &forest);
      }
   }

        while (tmp->left&&tmp->right != NULL)
      {
         
          leftP = deleteMin(&forest);
          rightP = deleteMin(&forest);
          tmp->left = leftP;
          tmp->right = rightP;
          tmp = MakeNode(top->symbol, top->weight, tmp->left, tmp->right);
          pqInsert(tmp, &forest);
      }
      return tmp;
{
0
 
LVL 16

Accepted Solution

by:
AlexNek earned 2000 total points
ID: 18873653
>converting it to C is where I am having the problem.
It can't be a big problem. Post the pseudo code and notice the parts with troubles.

>...in hopes of getting criticism
This lines look not so good for me.
          tmp->left = leftP;
          tmp->right = rightP;

          tmp = MakeNode(top->symbol, top->weight, tmp->left, tmp->right);
You assign unassigned variable /at least I can't see where it was/, fill the fields and then assign variable.

I have a small notices in addition. I don't like:
- function parameters like int freqs[256
- variables declaration in one line TreeNode* leftP, *rightP, *tmp;
- such a logical expression while (tmp->left&&...
0
 
LVL 84

Expert Comment

by:ozo
ID: 18880541
top->weight and top->symbol also seem to be referencing an undefined pointer
what is MakeNode, and how  are TreeNode and TreeEntry defined?
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