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+#advent of code 2020
+#day 16
+#I spent a lot of time fixing its logic during solving
+#so the code was cleaned thorougly after finishing
+#which was a good idea because i was doing it directly after
+#and still have to think for a minute what some lines are actually doing
+#I think there's a way to skip looping over tickets for second time
+#but it would make it unnecessarily convoluted
+#I also tried making understandable variable names  way too hard for a puzzle code
+p1 = 0; 
+p2 = 1; 
+requirements = dict();
+NearbyTickets = [];
+PuzzleInput = open("16.in","r").read().split("\n\n");
+#rules for ticket fields
+for line in PuzzleInput[0].split("\n"): 
+	FieldName, FieldValues = line.split(":");
+	FieldValues = [ tuple([int(v) for v in fv.split("-")]) for fv in FieldValues.split(" or ")];
+	requirements[FieldName] = FieldValues;
+#your ticket
+MyTicket = [int(val) for val in PuzzleInput[1].split("\n")[1].split(",")]; 
+#nearby tickets
+for line in PuzzleInput[2].split("\n")[1:]:
+	if len(line) <= 1: continue;
+	NearbyTickets.append([int(val) for val in line.split(",")]);
+
+GoodTickets = [];
+for ticket in NearbyTickets:
+	ValidTicket = True;
+	for TicketValue in ticket:
+		for FieldValues1, FieldValues2 in requirements.values():
+			test1 = FieldValues1[0] <= TicketValue <= FieldValues1[1];
+			test2 = FieldValues2[0] <= TicketValue <= FieldValues2[1];
+			valid = test1 or test2;
+			if valid: break;
+		if not valid:
+			p1 += TicketValue;
+			ValidTicket = False;
+	if ValidTicket: GoodTickets.append(ticket);
+
+Fields = dict();
+InvalidFields = dict();
+#find for which fields the numbers in tickets are viable for 
+#store them in InvalidFields dict
+for ticket in GoodTickets:
+	for ti, TicketValue in enumerate(ticket):
+		for FieldName in requirements:
+			if FieldName in Fields.values(): continue;
+			FieldValues1, FieldValues2 = requirements[FieldName];
+			test1 = FieldValues1[0] <= TicketValue <= FieldValues1[1];
+			test2 = FieldValues2[0] <= TicketValue <= FieldValues2[1];
+			valid = test1 or test2;
+			if not valid:
+				if FieldName not in InvalidFields: InvalidFields[FieldName] = set();
+				InvalidFields[FieldName].add(ti);
+
+#all fields have different number of possible places and its linear
+#that is: field 1 has 19/20 possible assignments, field 2 has 18/20 etc.
+#by sorting it from longest to shortest we make assign the fields in a single loop
+#check which indexes are missing and skip the indexes that have their field assigned
+for FieldName in sorted(InvalidFields, key = lambda f: len(InvalidFields[f]) , reverse=True): 
+	FieldIndexes = [FieldIndex for FieldIndex in range(len(requirements)) if FieldIndex not in InvalidFields[FieldName]];
+	FieldIndexes = [FieldIndex for FieldIndex in FieldIndexes if FieldIndex not in Fields]; #trim already assigned fields
+	Fields[FieldIndexes[0]] = FieldName;
+
+for key in Fields:
+	if "departure" in Fields[key]: p2 *= MyTicket[key]; 
+
+print("part 1 =",p1); 
+print("part 2 =",p2);
+