OpenEuphoria

Re: Project Programmer Wanter

• Posted by CChris <christian.cuvier at agricultur?.go?v.fr> Feb 12, 2008
• 938 views

CChris wrote:
> 
> Ret Law wrote:
> > 
> > That sounds good.
> > 
> > Basically what I want is to create output, both as a data text file and as
> > screen
> > display of the full permutation of a given number of items over a given
> > number
> > of digits according to a given rule of sucession.
> > 
> > For example:
> > 
> > Items:
> > A,B,C,D
> > 
> > # of Digits:
> > 3
> > 
> > Order:
> > A,B,C,D, beginning with AAA, ending with DDD and rotating in successive
> > order
> > across right to left.
> > 
> > Output:
> > AAA
> > AAB
> > AAC
> > AAD
> > ABA
> > ABB
> > ABC
> > ABD
> > ACA
> > ACB
> > ACC
> > ACD
> > BAA
> > BAB
> > BAC
> > BAD
> > BBA
> > BBB
> > BBC
> > BBD
> > BCA
> > BCB
> > BCC
> > BCD
> > BDA
> > BDB
> > BDC
> > BDD
> > CAA
> > CAB
> > CAC
> > CAD
> > CBA
> > CBB
> > CBC
> > CBD
> > CCA
> > CCB
> > CCC
> > CCD
> > CDA
> > CDB
> > CDC
> > CDD
> > DAA
> > DAB
> > DAC
> > DAD
> > DBA
> > DBB
> > DBC
> > DBD
> > DCA
> > DCB
> > DCC
> > DCD
> > DDA
> > DDB
> > DDC
> > DDD
> > 
> > How would that function be implemented to achieve that?
> 

Here is a modified implementation that doesn't keep the whole data in memory,
writes both item and symmetric item. It assumes the objects whose arrangements
are to be written are byte sized:

function update_counter(
    sequence counter,  -- counter sequence to increment
    integer start_val, -- usually 1
    integer end_val,   -- usually len
    integer len)       -- counter assumed length
-- increments len counters right to left, returns {} if done or
-- new counter & rank of first value changed.
  if not length(counter) then
    -- main function will make this call at startup
    -- create initial value of counter
    return repeat(start_val,len) & len
  elsif length(counter)!=len+1 then
    return 0 -- shouldn't happen
  end if
-- assert: start_val <= end_val
  for i=len to 1 by -1 do -- all counters have same length, len+1
    if counter[i] < end_val then
      counter[i]+=1
      counter[$]=i -- rank of first value changed
      return counter 
    else
      counter[i] = start_val
    end if
  end for
  return {} -- the end, or len<=0
end function

global procedure enumerate(
    sequence succession, -- list of objects to appear in order
    integer n,         -- number of digits
    sequence outfile)    -- output file name
-- WARNING: no check is made for available space on the medium you write to. 
-- Writing a file that's too big may result in data loss or physical damage 
-- to medium.
-- AUTHOR WILL DECLINE ANY CLAIM FOR LIABILITY.
  sequence counter,rev_item,item
  integer ls,fh
  
  ls=length(succession)
  counter=update_counter("",1,ls,n)
  item=repeat(0,n)
  rev_item=repeat(0,n)
  fh=open(outfile,"wb")
  if fh=-1 then
    puts(2,"Could not open output file - bailing out")
    return
  end if
-- The first byte in the output file is the length of each item. 
-- Remove the next statement if it will always be 4, for instance
  puts(fh,n)
  while compare(counter,{})=1 do
    for i=counter[$] to n do
      item[i]=succession[counter[i]]
      rev_item[i]=succession[$+1-counter[i]]
    end for
    puts(fh,item)
    puts(fh,rev_item)
    counter=update_counter(counter,1,ls,n)
  end while
  close(fh)
end procedure

global procedure display_output(sequence infile)
-- reads what enumerate() has written
  integer fh,n
  sequence item,rev_item

  fh=open(infile,"rb")
  if fh=-1 then
    puts(2,"Couldn't locate input file - bailing out.")
    return
  end if
-- replace next statement with a fixed assignment like n=4 if you removed
-- the puts(fh,n) statement in enumerate().
  n=getc(fh) -- record length
  while 1 do
    item=get_bytes(fh,n)
    if not length(item) then-- normal termination
      exit
    elsif length(item)<n then
      puts(2,"Input file doesn't hold properly matched strings - halting.")
      exit
    end if
    rev_item=get_bytes(fh,n)
    if length(rev_item)<n then
      puts(2,"Input file doesn't hold properly matched strings - halting.")
      exit
    end if
    -- change this statement in order to meet your display requirements
    printf(1,"%s %s\n",{item,rev_item})
  end while
  close(fh)
end procedure  

 

CChris