Move-to-front algorithm: Difference between revisions

Line 2,131:

<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 /*(offset) for this task's requirement.*/

one= 1 /*(offset) for this task's requirement.*/

do j=1 for words(xxx); x=word(xxx, j) /*process a single word at a time. */

do j=1 for words(xxx); x= word(xxx, j) /*process a single word at a time. */

@= 'abcdefghijklmnopqrstuvwxyz'; @@=@ /*symbol table: the lowercase alphabet */

@= '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. */

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. */

_= pos(z, @); if _==0 then iterate /*the symbol position in symbol table. */

$=$ (_ - one); @=z || delstr(@, _, 1) /*(re─)adjust the symbol table string. */

$= $ (_ - 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. */

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= substr(@@, n, 1); != ! || y /*the decode symbol for the N word.*/

@@=y || delstr(@@, n, 1) /*rebuild the symbol table string. */

@@= 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>

<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>