Day 24 part 1 done!

2021/nim/day24.nim

@@ -1,73 +1,28 @@
 import ./common, std/[strutils, sugar, sequtils, options, tables, sets, strformat, algorithm, pegs]
 
-type
-  Register = int
-  ALUInstruction = (string, Register, string)
-  ALUState = array[4, int]
-
-proc parseInstruction(s: string): ALUInstruction =
-  # echo s
+proc parseInstructionArg(s: string): int =
   let ss = s.split(' ')
-  let i = if ss.len > 2: ss[2] else: ""
-  (ss[0], ss[1][0].ord - ord('w'), i)
-
-proc runALUInstructions(instructions: seq[ALUInstruction], input: string): ALUState =
-  var inputs = input.reversed
-  let registers = toHashSet(['w', 'x', 'y', 'z'])
-  var n = 0
-  for i in instructions:
-    let (op, reg, arg) = i
-    var narg = arg
-    var num = 0
-    if arg != "":
-      if registers.contains(arg[0]):
-        let index = arg[0].ord - 'w'.ord
-        num = result[index]
-        narg = &"r{index+1}"
-      else: num = arg.parseInt
-    if n mod 18 in [4, 5, 15, 0]: 
-      echo &"{result} -> {op} {narg} to r{reg+1} (Input Left: {inputs.join})"
-    case op:
-      of "inp": result[reg] = inputs.pop.ord - '0'.ord
-      of "add": result[reg] += num
-      of "mul": result[reg] *= num
-      of "div": result[reg] = result[reg] div num
-      of "mod": result[reg] = result[reg] mod num
-      of "eql": result[reg] = (result[reg] == num).int
-    inc n
+  if ss.len > 2 and not (ss[2][0] in 'w'..'z'): ss[2].parseInt
+  else: 0
 
 proc p1(input: Lines): uint64 =
-  # repeating these 18 instructions:
-  # w is used to store the input digit
-  # x is zeroed
-  # z is added to x
-  # x is modulo'd over 26
-  # z is divided by either 1 or 26 (mostly in the latter half of the inputs)
-  # x is added with SOME NUMBER (sometimes negative)
-  # x is ALWAYS eql'd with w and 0
-    # this is meant to ensure that x is NOT equal to the input?
-  # y is ALWAYS set to 25
-  # y is multiplied by x, which will be 25 if x was 1 or 0 otherwise
-    # so y will be 25 if x was equal to the input and 0 if not
-  # y is incremented
-    # 26 now, if x was equal, 1 if not
-  # z is multiplied by y
-    # so z
-  # y is zeroed out, set to w (the input), added with SOME NUMBER, then multiplied with x
-  # add y to z
-
-  # if I need to get z to zero, I need to know where those 26-divisions are and leverage them
-  # if I can ever get y to be negative, that could help a lot as well
-
-  # probably a relatively simple way to bruteforce over this?
-  let instructions = input.map(parseInstruction)
-  # let oalu = instructions.runALUInstructions("13579246899999")
-  # echo oalu
-  let alu = instructions.runALUInstructions("99879249111111")
-  echo alu
-  0
-
-proc p2(input: Lines): uint64 =
-  0
+  let instructionArgs = input.map(parseInstructionArg)
+  var reversedDigits = initTable[int, int]()
+  var cantComputeYet: seq[(int, int)] = @[]
+  for i in 0..13:
+    let o = i * 18
+    if instructionArgs[o+4] == 26:
+      let (previousI, previousAddend) = cantComputeYet.pop
+      let diff = previousAddend + instructionArgs[o+5]
+      echo diff
+      echo previousI
+      if diff < 0:
+        reversedDigits[previousI] = 9
+        reversedDigits[i] = 9 + diff
+      else:
+        reversedDigits[previousI] = 9 - diff
+        reversedDigits[i] = 9
+    else: cantComputeYet.add (i, instructionArgs[o+15])
+  reversedDigits.keys.toSeq.sorted.mapIt($reversedDigits[it]).join().parseBiggestUInt()
 
 time(&"Day 24 Part 1"): echo 24.loadInput.p1