1 files changed, 69 insertions, 0 deletions
diff --git a/2020/sixteen.nim b/2020/sixteen.nim
new file mode 100644
index 0000000..4896c38
--- /dev/null
+++ b/2020/sixteen.nim
@@ -0,0 +1,69 @@
+# Day Sixteen: Ticket Translation
+import std/[os, strutils, sequtils, sugar]
+
+let input: string = paramStr(1)
+
+type Rule = tuple[field: string, values: seq[int]]
+
+let data: seq[string] = readFile(input).split("\n\n")
+let rules: seq[Rule] =
+  data[0].split("\n")
+    .map(foo => (foo.split(": ")[0], foo.split(": ")[1].split(" or ")
+      .foldl(a & countup(b.split("-")[0].parseInt(),
+        b.split("-")[1].parseInt()).toSeq(), @[-1])[1..^1]))
+let ticket: seq[int] =
+  data[1].split("\n")[1].split(",")
+    .map(parseInt)
+let nearby: seq[seq[int]] =
+  data[2].strip().split(":\n")[1].split("\n")
+    .map(foo => foo.strip().split(",").map(parseInt))
+
+var min = rules[0][1].min
+var max = rules[0][1].max
+for rule in rules:
+  min = min(rule[1].min, min)
+  max = max(rule[1].max, max)
+
+proc validate(tickets: seq[seq[int]], min: int, max: int): int =
+  for ticket in tickets:
+    for value in ticket:
+      if value < min or value > max:
+        result += value
+
+echo nearby.validate(min, max)
+
+proc purge(tickets: seq[seq[int]], min: int, max: int): seq[seq[int]] =
+  for ticket in tickets:
+    if ticket.allIt(it < max) and ticket.allIt(it > min):
+      result.add(ticket)
+
+proc flip(tickets: seq[seq[int]]): seq[seq[int]] =
+  for i in 0 ..< tickets[0].len():
+    var foo: seq[int]
+    for ticket in tickets:
+      foo.add(ticket[i])
+    result.add(foo)
+
+var possibilities: seq[seq[string]]
+for i, field in nearby.purge(min, max).flip():
+  var foo: seq[string]
+  for rule in rules:
+    if field.allIt(it in rule.values):
+      foo.add(rule.field)
+  possibilities.add(foo)
+
+proc determine(order: seq[string]): seq[string] =
+  if order.len() == ticket.len:
+    return order
+  for value in possibilities[order.len]:
+    if value notin order:
+      result = determine(order & value)
+      if result.len != 1:
+        return result
+  return @["fail"]
+
+var order: seq[string]
+
+echo zip(determine(order), ticket)
+  .filterIt(it[0].contains("departure"))
+  .foldl(a * b[1], 1)