27 lines
2.4 KiB
Rexx
27 lines
2.4 KiB
Rexx
/*REXX pgm computes a Recamán sequence up to N; the 1st dup; # terms for a range of #'s.*/
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parse arg N h . /*obtain optional arguments from the CL*/
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if N=='' | N=="," then N= 15 /*Not specified? Then use the default.*/
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if h=='' | h=="," then h= 1000 /* " " " " " " */
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say "Recamán's sequence for the first " N " numbers: " recaman(N)
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say; say "The first duplicate number in the Recamán's sequence is: " recaman(0)
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say; say "The number of terms to complete the range 0───►"h ' is: ' recaman(-h)
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exit 0 /*stick a fork in it, we're all done. */
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/*──────────────────────────────────────────────────────────────────────────────────────*/
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recaman: procedure; parse arg y,,d.; $=0; !.=0; _=0; !.0=1 /*init. array and vars.*/
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r= y<0; Reca= 0; hi= abs(y) /*for the 2nd invoke. */
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o= y==0; if y<1 then y= 1e8 /* " " 3rd " */
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do #=1 for y-1; z= _ - # /*next # might be < 0. */
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if z<0 then z= _ + # /*this is faster than: */
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else if !.z then z= _ + # /*if !.z | z<0 then ···*/
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!.z= 1; _= z /*mark it; add to seq.*/
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if r then do; if z>hi then iterate /*ignore #'s too large.*/
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if d.z=='' then Reca= Reca + 1 /*Unique? Bump counter.*/
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d.z= . /*mark # as a new low. */
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if Reca>=hi then return # /*list is complete ≥ HI*/
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iterate
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end /* [↑] a range of #s. */
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if o then do; if d.z==. then return z; d.z=.; iterate /*check if dup #.*/
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end
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$= $ z /*add number to $ list?*/
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end /*#*/; return $ /*return the $ list. */
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