advent-of-code-2025/D2P1.rex at main · exoboosters/advent-of-code-2025 · GitHub

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/* Rexx */
/* Advent of Code 2025 - Mainframe Edition */
/* Day : 02 / Part : 01 */
/* Description : Given a list of input ProductIDs in a range form    */
/*               identify invalid IDs. They are the form of a repeat-*/
/*               -ed sequence of numbers like 55 or 11221122. Add the*/
/*               invalid IDs to get the clue for Part 2              */
/* Algo : Read input file (single record)
          Parse into individual ranges
          Split range into lower & upper index to check
          If length of number is odd, it can't be invalid! Skip
          If even, split it into half and compare both sides
          If same, InvalidID. Add to total
          Display total */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
NUMERIC DIGITS 15
total = 0
/* Read file */
Address TSO
  "alloc da('D2P1.TEXT') fi(prod) shr reuse"
  "execio * diskr prod (stem recs. finis"
  "free fi(prod)"
/* Outer loop for parsing the ranges */
inpt = recs.1
parse var inpt range ',' inpt
Do while inpt <> ''
   parse var inpt strt '-' endn . /* Drop any extra stuff, should be nothing */
   say 'Range' inpt || '. Starting' strt 'to' endn
   Do inL = strt to endn
      If length(inL) // 2 = 1 Then Iterate
      fhalf = left(inL,length(inL)/2)
      shalf = right(inL,length(inL)/2)
      If fhalf = shalf Then Do
      /* say 'Invalid ProductID' inL */
         total = total + inL
      End
   End
   parse var inpt range ',' inpt
End