mirror of
https://github.com/Threnklyn/advent-of-code-go.git
synced 2026-06-06 20:30:12 +02:00
alexchao26
121 lines
3.2 KiB
Python
121 lines
3.2 KiB
Python
from collections import defaultdict
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def day5(input: str, part: int) -> int:
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split_input = input.split("\n\n")
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reversed_graph: defaultdict[int, list[int]] = defaultdict(list)
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for line in split_input[0].splitlines():
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rule_parts = line.split("|")
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X, Y = int(rule_parts[0]), int(rule_parts[1])
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reversed_graph[Y].append(X)
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updates: list[list[int]] = [
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[int(x) for x in line.split(",")] for line in split_input[1].splitlines()
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]
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part1_ans: int = 0
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# for part 2
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invalid_updates: list[list[int]] = []
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for update in updates:
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# assuming there are no repeat updates...
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seen_set: set[int] = set()
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disallowed_set: set[int] = set()
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is_valid = True
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for num in update:
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if num in disallowed_set:
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is_valid = False
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break
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for cannot_come_before in reversed_graph[num]:
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if not cannot_come_before in seen_set:
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disallowed_set.add(cannot_come_before)
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seen_set.add(num)
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if is_valid:
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part1_ans += update[len(update) // 2]
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else:
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invalid_updates.append(update)
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if part == 1:
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return part1_ans
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# part2
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# can assume there's only one valid order... or that unordered ones will not affect the middle value
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# so just take all the numbers and create the correct order by traversing the graph of dependencies?
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part2_ans: int = 0
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for update in invalid_updates:
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correct_order: list[int] = []
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all_nums: set[int] = set(update)
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used_nums: set[int] = set()
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while len(all_nums) > len(used_nums):
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for num in all_nums:
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if num in used_nums:
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continue
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if not num in reversed_graph:
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correct_order.append(num)
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# all_nums.remove(num)
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used_nums.add(num)
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continue
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# check if all of this num's dependencies are in used_nums
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# or if its dependencies are not present at all
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# there's definitely a better algo for this...
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if all(
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[
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dep in used_nums or not dep in all_nums
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for dep in reversed_graph[num]
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]
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):
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correct_order.append(num)
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# all_nums.remove(num)
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used_nums.add(num)
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continue
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part2_ans += correct_order[len(correct_order) // 2]
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return part2_ans
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# page ordering rules, X|Y -> X must come before Y
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# updates, basically orders of pages
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# missing page numbers are ignored..
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# part1_ans: sum middle page of each valid update
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example = """47|53
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97|13
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97|61
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97|47
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75|29
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61|13
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75|53
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29|13
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97|29
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53|29
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61|53
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97|53
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61|29
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47|13
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75|47
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97|75
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47|61
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75|61
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47|29
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75|13
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53|13
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75,47,61,53,29
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97,61,53,29,13
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75,29,13
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75,97,47,61,53
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61,13,29
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97,13,75,29,47"""
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input = open("input.txt").read()
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print(f"day5 example: {day5(example,1)} want 143")
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print(f"day5: {day5(input,1)} want 5166")
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print(f"part2 example: {day5(example,2)} want 123")
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print(f"part2: {day5(input,2)} want 4679")
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