1 files changed, 121 insertions, 0 deletions

diff --git a/day13/solution.nim b/day13/solution.nim
new file mode 100644
index 0000000..901e646
--- /dev/null
+++ b/day13/solution.nim
@@ -0,0 +1,121 @@
+import strutils
+import strformat
+import algorithm
+
+type
+  Data = ref object
+    val: int
+    list: seq[Data]
+
+  Packet = tuple
+    first: Data
+    second: Data
+
+  Input = seq[Packet]
+
+proc `$`(data: Data): string =
+  if data.val != -1:
+    return fmt"{data.val}"
+
+  result = "[" & data.list.join(",") & "]"
+
+proc parseData(strData: string, i: var int): Data =
+  result = Data(val: -1, list: newSeq[Data]())
+  let dataLen = strData.len()
+  while i < dataLen:
+    case strData[i]:
+      of '[':
+        i += 1
+        result.list.add(parseData(strData, i))
+      of ']':
+        i += 1
+        return result
+      of ',':
+        i += 1
+      else:
+        var j = i
+        while j < dataLen and strData[j].isDigit():
+          j += 1;
+        let toPush = Data(val: strData[i..<j].parseInt())
+        result.list.add(toPush)
+        i = j
+
+proc parsePacket(strPacket: string): Packet =
+  let strDatas = strPacket.splitLines()
+  assert(strDatas.len() == 2)
+  var
+    i0 = 0
+    i1 = 0
+  result = (parseData(strDatas[0][1..^2], i0), parseData(strDatas[1][1..^2], i1))
+
+proc parseFile(content: string): Input =
+  let strPackets = content.strip().split("\n\n")
+
+  for strPacket in strPackets:
+    result.add(parsePacket(strPacket))
+
+proc compare(A, B: int): int =
+  if A < B: return -1
+  elif A > B: return 1
+  else: return 0
+
+proc dataListForm(data: Data): Data =
+  # Check if its already in list form
+  if data.val == -1:
+    return data
+  result = Data(val: -1, list: @[data])
+
+proc compare(A, B: Data): int =
+  # Both numbers:
+  if A.val != -1 and B.val != -1:
+    return compare(A.val, B.val)
+
+  # Transform both data to list form
+  let
+    A = dataListForm(A)
+    B = dataListForm(B)
+
+  assert(A.val == -1 and B.val == -1)
+  # Both are lists now
+  let
+    li = A.list.len()
+    lj = B.list.len()
+    N = min(li, lj)
+
+  var i = 0
+  while i < N:
+    let res = compare(A.list[i], B.list[i])
+    if res != 0:
+      return res
+    i += 1
+
+  return compare(li, lj)
+
+proc part1(Packets: Input): int =
+  for i, packet in Packets:
+    # echo fmt"Checking packet {packet}"
+    let comparison = compare(packet.first, packet.second)
+    # echo fmt"result = {comparison}"
+    if comparison < 0:
+      result += i+1
+
+proc part2(Packets: Input): int =
+  let driverPackets = parseFile("[[6]]\n[[2]]\n")
+  let first = driverPackets[0].first
+  let second = driverPackets[0].second
+  var datas = @[first, second]
+
+  for packet in Packets:
+    datas.add(packet.first)
+    datas.add(packet.second)
+
+  datas.sort(compare)
+  let firstIndex = datas.binarySearch(first, compare) + 1
+  let secondIndex = datas.binarySearch(second, compare) + 1
+  return firstIndex * secondIndex
+
+let content = readFile("./input.txt")
+let input = parseFile(content)
+
+echo part1(input)
+echo part2(input)