2023 Day 15 Part 2

2023/day15.nim

@@ -33,21 +33,81 @@ func join[T](parts: seq[seq[T]], sep: T): seq[T] =
     result.add sep
     result &= part
 
+type Op = enum
+  Dash
+  Equals
+
+func parseOp(c: char): Op =
+  case c:
+    of '-': Dash
+    of '=': Equals
+    else: result
+
+type Step = tuple
+  text: string
+
+  label: string
+  op: Op
+  num: int
+
+func parseStep(text: string): Step =
+  result.text = text
+
+  if scanf(text, "$+=$i$.", result.label, result.num):
+    result.op = Equals
+    return
+
+  if scanf(text, "$+-$.", result.label):
+    result.op = Dash
+    return
+
 type Init = tuple
-  steps: seq[string]
+  steps: seq[Step]
 
 func parseInit(text: string): Init =
-  result.steps = text.strip.split(',')
+  result.steps = text.strip.split(',').map(parseStep)
 
-func hash(step: string): int =
+func hash(text: string): int =
-  for c in step:
+  for c in text:
     result = ((result + c.ord) * 17) mod 256
 
 proc part1(input: string): int =
   let text = readFile(input)
   let init = parseInit(text)
 
-  init.steps.map(hash).sum
+  init.steps.mapIt(it.text.hash).sum
+
+type HASHMAP = object
+  boxes: array[0..255, OrderedTable[string, int]]
+
+func remove(h: var HASHMAP, label: string) =
+  let box = label.hash
+  h.boxes[box].del label
+
+func insert(h: var HASHMAP, label: string, focusLength: int) =
+  var box = label.hash
+  h.boxes[box][label] = focusLength
+
+func exec(h: var HASHMAP, step: Step) =
+  case step.op:
+    of Dash: h.remove(step.label)
+    of Equals: h.insert(step.label, step.num)
+
+func power(h: HASHMAP): int =
+  for (i, box) in enumerate(h.boxes):
+    for (j, focalLength) in enumerate(box.values):
+      result.inc (i + 1) * (j + 1) * focalLength
+
+proc part2(input: string): int =
+  let text = readFile(input)
+  let init = parseInit(text)
+
+  var hashmap: HASHMAP
+  for step in init.steps:
+    hashmap.exec step
+  hashmap.power
 
 echo part1("input/test.txt")
 echo part1("input/day15.txt")
+echo part2("input/test.txt")
+echo part2("input/day15.txt")