day08

2023/day08.nim

@@ -0,0 +1,59 @@
+import std/[sequtils, strscans, strutils, sugar, tables]
+
+type
+  Map = tuple
+    instructions: string
+    nodes: Table[string, tuple[l: string, r: string]]
+
+func walk(map: Map, startingNodes: seq[string]): int =
+  let il = map.instructions.len
+  var
+    p = 0
+    nodes = startingNodes
+  while true:
+    let i = map.instructions[p mod il]
+    nodes = block:
+      var newNodes: seq[string]
+      if i == 'L':
+        for node in nodes:
+          newNodes.add(map.nodes[node].l)
+      else:
+        for node in nodes:
+          newNodes.add(map.nodes[node].r)
+      newNodes
+    p += 1
+    if nodes.allIt(it[^1] == 'Z'):
+      return p
+    if p mod 1_000_000 == 0:
+      debugEcho p
+
+func parse(input: string): Map =
+  let
+    sp = input.split("\n\n")
+    nodeLines = sp[1].splitLines
+  result.instructions = sp[0]
+
+  var n, l, r: string
+  for line in nodeLines:
+    discard scanf(line, "$* = ($*, $*)", n, l, r)
+    result.nodes[n] = (l, r)
+
+proc p1(input: string) =
+  let startingNodes = @["AAA"]
+  echo input.parse().walk(startingNodes)
+
+proc p2(input: string) =
+  let
+    map = input.parse()
+  let
+    startingNodes = collect:
+      for k in map.nodes.keys:
+        if k[^1] == 'A':
+          k
+  echo startingNodes
+  echo map.walk(startingNodes)
+
+when isMainModule:
+  let input = stdin.readAll().strip()
+  p1(input)
+  #p2(input)  # takes too much time