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Sorting algorithms/Heapsort: Difference between revisions
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This REXX version uses a heapsort to sort elements of an array, the elements can be numbers or strings.
<br>Indexing of the array (for this version) starts with '''1''' (one), but can be programmed to start with zero.
<lang rexx>/*REXX
@.=; @.1='alpha' ; @.6 ='zeta' ; @.11='lambda' ; @.16='pi' ; @.21='phi'
@.2='beta' ; @.7 ='eta' ; @.12='mu' ; @.17='rho' ; @.22='chi'
@.3='gamma' ; @.8 ='theta'; @.13='nu' ; @.18='sigma' ; @.23='psi'
@.4='delta' ; @.9 ='iota' ; @.14='xi' ; @.19='tau' ; @.24='omega'
@.5='epsilon'; @.10='kappa'; @.15='omicron'; @.20='upsilon'
do #=1 while @.#\==''; end; #=#-1 /*find # entries.*/
call show "before sort:"
call heapSort
call show " after sort:"
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
heapSort: procedure expose @.; parse arg n; do j=n%2 by -1 to 1
call shuffle j,n
end /*j*/
do n=n by -1 to 2
_=@.1; @.1=@.n; @.n=_;
end /*n*/
return
/*──────────────────────────────────────────────────────────────────────────────────────*/
shuffle: procedure expose @.; parse arg i,n; $=@.i /*obtain the parent*/
do while i+i<=n; j=i+i; k=j+1
if k<=n then if @.k>@.j then j=k
if $>=@.j then leave
@.i=@.j; i=j
end /*while*/
@.i=$; return
/*──────────────────────────────────────────────────────────────────────────────────────*/
show: do e=1 for #; say ' element' right(e,length(#)) arg(1) @.e; end; return</lang>
''output''' using the (default) Greek alphabet for input:
<pre>
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===version 2===
This REXX version creates a stemmed array from a list.
<lang rexx>/*REXX
g
do #=1 for words(g); @.#=word(g,#); end; #=#-1
call show "before sort:"
call heapSort
call show " after sort:"
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
heapSort: procedure expose @.; parse arg n; do j=n%2 by -1 to 1
call shuffle j,n
end /*j*/
do n=n by -1 to 2
_=@.1; @.1=@.n; @.n=_;
end /*n*/
return
/*──────────────────────────────────────────────────────────────────────────────────────*/
shuffle: procedure expose @.; parse arg i,n; $=@.i /*obtain the parent*/
do while i+i<=n; j=i+i; k=j+1
if k<=n then if @.k>@.j then j=k
if $>=@.j then leave
@.i=@.j; i=j
end /*while*/
@.i=$; return
/*──────────────────────────────────────────────────────────────────────────────────────*/
show: do e=1 for #; say ' element' right(e,length(#)) arg(1) @.e; end; return</lang>
'''output''' is the same as the 1<sup>st</sup> REXX version.
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