AoC 2024 day 5 part 1

aoc2024/src/day05/python/solution.py

@@ -0,0 +1,51 @@
+# Copyright 2024 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from collections import defaultdict
+from typing import Sequence
+
+# Tracks pages to downstream pages.
+type RuleGraph = defaultdict[int, set]
+
+
+def _generate_graph(order_rules: Sequence[str]) -> RuleGraph:
+  """Generates graph from order rules. A|B means A precedes B."""
+  graph = defaultdict(set)
+  for rule in order_rules:
+    first, second = map(int, rule.split('|'))
+    graph[first].add(second)
+  return graph
+
+
+def _is_valid(graph: RuleGraph, update: Sequence[int]) -> bool:
+  """Returns true if an update (sequence of pages) complies with rules."""
+  if len(update) == 1:
+    return True
+  curr_page = update[0]
+  next_page = update[1]
+  if curr_page not in graph:
+    return False
+  children = graph.get(curr_page)
+  if next_page not in children:
+    return False
+  return _is_valid(graph, update[1:])
+
+
+def sum_middle_pages(input: Sequence[str]) -> int:
+  """Sums the middle page of all the valid updates."""
+  breakline_num = list(input).index('')
+  graph = _generate_graph(input[:breakline_num])
+  updates = (list(map(int, input[i].split(',')))
+             for i in range(breakline_num + 1, len(input)))
+  return sum(update[len(update) // 2] if _is_valid(graph, update) else 0
+             for update in updates)

aoc2024/test/day05/python/example1.txt

@@ -0,0 +1,28 @@
+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47