Part 1 solution for Day 5.

day5/solver.py

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+from collections.abc import Iterable
+import operator as op
+import itertools as it
+from collections import defaultdict
+from typing import Iterator, TypeAlias
+import logging
+import sys
+
+logger = logging.getLogger()
+logger.addHandler(logging.StreamHandler())
+
+
+RuleSet: TypeAlias = dict[str, set[str]]
+
+
+def parse_rules(rule_lines: Iterable[str]) -> RuleSet:
+    """
+    Parse a sequence of poset rules into a rulset
+    mapping id -> list of descendents.
+    """
+    descendents = defaultdict(set)
+    for line in rule_lines:
+        if '|' not in line:
+            raise ValueError(f"Provided line '{line}' is not a rule.")
+        a, b = line.split('|')
+        descendents[a].add(b)
+    return descendents
+
+def check_line(line: list[str], ruleset: RuleSet) -> bool:
+    """
+    Check whether the provided line satisfies the given rules.
+    """
+    for i, char in enumerate(line):
+        rules = ruleset[char]
+        if any(prevchar in rules for prevchar in line[:i]):
+            return False
+
+    return True
+
+def get_middle(line: list[str]) -> str:
+    """
+    Get the middle of the line, if it exists.
+    """
+    if not len(line) % 2:
+        raise ValueError("Even length line has no middle.")
+    return line[len(line) // 2]
+
+def process_data(lines: Iterator[str]):
+    lines = map(op.methodcaller('strip'), lines)
+    lines = it.dropwhile(op.not_, lines)
+    ruleset = parse_rules(it.takewhile(bool, lines))
+    if logger.isEnabledFor(logging.DEBUG):
+        logger.debug(f"Ruleset: {ruleset}")
+
+    total = 0
+    for line in lines:
+        if line:
+            parts = line.split(',')
+            if check_line(parts, ruleset):
+                total += int(get_middle(parts))
+                logger.debug(f"Valid line: {line}")
+            else:
+                logger.debug(f"Invalid line: {line}")
+
+    return total
+
+
+def main():
+    with open(sys.argv[1]) as f:
+        total = process_data(f)
+        print(f"Total middle-sum is {total}")
+
+
+if __name__ == '__main__':
+    main()