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fix for quadratic time caused by substring() in LZW compression #114

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inflaton opened this issue Feb 6, 2022 · 0 comments
Open

fix for quadratic time caused by substring() in LZW compression #114

inflaton opened this issue Feb 6, 2022 · 0 comments

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@inflaton
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inflaton commented Feb 6, 2022

Hi Kevin,

I've made a fix for quadratic time caused by substring() in LZW compression. The key to the fix is to use a new overloaded method TST.longestPrefixOf(String query, int startIndex) in LZW.compress() method. Attached please find 3 reference files:

  1. LempelZivWelch.java: improved LZW.java

  2. TernarySearchTrie: improved TST.java

  3. lzw.sh: shell script proves the correctness and performance improvement.
    NOTE: existing LZW seems to take forever to compress dickens.txt (~29MB)

Regards,
Donghao

LZW_fix.zip
inflaton pushed a commit to inflaton/algs4 that referenced this issue Feb 6, 2022
@inflaton-ma
submitted issue: kevin-wayne/algs4#114
8ef0162
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