Day Eleven (Nim)

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+# Day 11: Monkey in the Middle
+import std/[os, strutils, sequtils, sugar, algorithm]
+import npeg # https://github.com/zevv/npeg
+
+let input = paramStr(1).readFile().strip().split("\n\n")
+
+type Monkey = object
+  stuff: seq[int]
+  inspect: (int) -> int
+  throw: (int) -> int
+  count: int
+
+var monkey: Monkey
+var monkees: seq[Monkey]
+
+let parser = peg(input):
+  input <- +(group * "\n\n")
+  group <- monkey * "\n" * starting * "\n" * operation * "\n" * test :
+    monkees.add(monkey)
+  monkey    <- "Monkey " * >Digit * ":":
+    monkey = Monkey()
+  starting  <- "  Starting items: " * >+Digit * *(", " * >+Digit):
+    monkey.stuff = capture[1 ..< capture.len].mapIt(parseInt(it.s))
+  operation <- "  Operation: new = old " * >("+" | "*") * " " * >("old" | +Digit):
+    let op =
+      if $1 == "+":
+        (x, y: int) => x + y
+      else:
+        (x, y: int) => x * y
+    if $2 == "old":
+      monkey.inspect = (x: int) => x.op(x)
+    else:
+      monkey.inspect = (x: int) => x.op(parseInt($2))
+  test      <- "  Test: divisible by " * >+Digit * "\n" * success * "\n" * failure:
+    monkey.throw = (x: int) => (if x mod parseInt($1) == 0: parseInt($2) else: parseInt($3))
+  success   <- "    If true: throw to monkey " * >Digit
+  failure   <- "    If false: throw to monkey " * >Digit
+
+assert parser.match(paramStr(1).readFile().strip()).ok == true
+
+let lcm = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29][0 ..< monkees.len].foldl(a*b, 1)
+
+var monkeys = monkees
+for _ in 0 ..< 20:
+  for i, monkey in monkeys:
+    while monkeys[i].stuff.len > 0:
+      var worry = monkeys[i].stuff.pop()
+      monkeys[i].count += 1
+      worry = monkeys[i].inspect(worry)
+      worry = worry div 3
+      monkeys[monkeys[i].throw(worry)].stuff.add(worry)
+
+echo monkeys.mapIt(it.count).sorted(Descending)[0..1].foldl(a*b, 1)
+
+monkeys = monkees
+for _ in 0 ..< 10000:
+  for i in 0 ..< monkeys.len:
+    while monkeys[i].stuff.len > 0:
+      var worry = monkeys[i].stuff.pop()
+      monkeys[i].count += 1
+      worry = monkeys[i].inspect(worry)
+      worry = worry mod lcm
+      monkeys[monkeys[i].throw(worry)].stuff.add(worry)
+
+echo monkeys.mapIt(it.count).sorted(Descending)[0..1].foldl(a*b, 1)