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for my project i have to create a huffman tree project, but my lecturer has said that i cannot use priority queues to build it? But i dunno how to implement that. Are there any other ways i can create a huffman tree without using priority queues?

This is an example of a huffman tree but it is using priority queues enter image description here enter image description here

Grant Sodipo
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    please consider [Why should I not upload images of code/data/errors?](https://meta.stackoverflow.com/questions/285551/why-should-i-not-upload-images-of-code-data-errors?r=SearchResults&s=1%7C98.8262) And can you explain what is a "*huffman tree project*" – user16320675 Nov 16 '22 at 16:52
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    ( BTW a PriorityQueue is basically just a list with the additional function of returning the smallest value [and some optimization for that] - so it can be replaced by a list and some code to retrieve the smallest value ) – user16320675 Nov 16 '22 at 17:44

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There's a trick that is often used to build Huffman trees in practice:

  1. Create a list of your symbols with probabilities, and sort it in ascending order

  2. Create an initially empty list for combined symbols. This will remain sorted as we work.

  3. While there is more than one symbol in the lists:

    1. Remove the two smallest symbols from the beginnings of two lists
    2. Combine them and add them to the end of the combined list. Because the new symbol has a higher combined probability than any combined symbol created before, this list remains sorted.

After the initial sorting, the smallest probability symbol will always be the first one of one of the two lists, so no priority queues or searching is required to find it.

This technique is quite clever, and your lecturer would not expect you to think of it yourself, so it was probably taught or referenced in class.

Matt Timmermans
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