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Move-to-front algorithm: Difference between revisions

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Move-to-front algorithm (view source)

Revision as of 18:26, 24 September 2020

9 bytes added ,  3 years ago
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<lang rexx>/*REXX program demonstrates the move─to─front algorithm encode/decode symbol table. */
parse arg xxx; if xxx='' then xxx= 'broood bananaaa hiphophiphop' /*use the default?*/
one=1 1 /*(offset) for this task's requirement.*/
do j=1 for words(xxx); x= word(xxx, j) /*process a single word at a time. */
@= 'abcdefghijklmnopqrstuvwxyz'; @@=@ @ /*symbol table: the lowercase alphabet */
$= /*set the decode string to a null. */
do k=1 for length(x); z= substr(x, k, 1) /*encrypt a symbol in the word. */
_= pos(z, @); if _==0 then iterate /*the symbol position in symbol table. */
$= $ (_ - one); @= z || delstr(@, _, 1) /*(re─)adjust the symbol table string. */
end /*k*/ /* [↑] the move─to─front encoding. */
!= /*set the encode string to a null. */
do m=1 for words($); n= word($, m) + one /*decode the sequence table string. */
y= substr(@@, n, 1); != ! || y /*the decode symbol for the N word.*/
@@= y || delstr(@@, n, 1) /*rebuild the symbol table string. */
end /*m*/ /* [↑] the move─to─front decoding. */
say ' word: ' left(x, 20) "encoding:" left($, 35) word('wrong OK', 1 + (!==x) )
end /*j*/ /*stick a fork in it, we're all done. */</lang>
{{out|output|text=&nbsp; when using the default input:}}
<pre>
word: broood encoding: 1 17 15 0 0 5 OK
word: bananaaa encoding: 1 1 13 1 1 1 0 0 OK
word: hiphophiphop encoding: 7 8 15 2 15 2 2 3 2 2 3 2 OK
</pre>
 
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