Day 5 part 2 solution.

day5/solver.py

@@ -10,6 +10,7 @@ logger = logging.getLogger()
 logger.addHandler(logging.StreamHandler())
 
 
+# Represents a DAG with maps a -> {descendents of a}
 RuleSet: TypeAlias = dict[str, set[str]]
 
 
@@ -37,6 +38,35 @@ def check_line(line: list[str], ruleset: RuleSet) -> bool:
 
     return True
 
+def sort_line(line: list[str], ruleset: RuleSet) -> list[str]:
+    """
+    Sort a given list of items by the given ruleset.
+    This actually returns the reverse sorted line.
+    """
+    sorted_line = []
+    visited = set()
+
+    while node := next((n for n in line if n not in visited), None):
+        _depth_sort_visit(node, line, ruleset, sorted_line, visited)
+
+    return sorted_line
+
+def _depth_sort_visit(
+        node: str, line: list[str], ruleset: RuleSet,
+        sorting: list[str], visited: set[str]
+):
+    """
+    Note we assume the graph is truly a DAG and has no cycles,
+    or this will create and infinite loop.
+    """
+    if node in visited:
+        return
+    for parent in ruleset[node].intersection(line):
+        _depth_sort_visit(parent, line, ruleset, sorting, visited)
+
+    visited.add(node)
+    sorting.append(node)
+
 def get_middle(line: list[str]) -> str:
     """
     Get the middle of the line, if it exists.
@@ -45,7 +75,7 @@ def get_middle(line: list[str]) -> str:
         raise ValueError("Even length line has no middle.")
     return line[len(line) // 2]
 
-def process_data(lines: Iterator[str]):
+def sum_correct_middles(lines: Iterator[str]):
     lines = map(op.methodcaller('strip'), lines)
     lines = it.dropwhile(op.not_, lines)
     ruleset = parse_rules(it.takewhile(bool, lines))
@@ -64,11 +94,33 @@ def process_data(lines: Iterator[str]):
 
     return total
 
+def sum_incorrect_middles(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 not check_line(parts, ruleset):
+                logger.debug(f"Invalid line: {line}")
+                corrected = sort_line(parts, ruleset)
+                logger.debug(f"Sorted line: {corrected}")
+                total += int(get_middle(corrected))
+
+    return total
+
 
 def main():
     with open(sys.argv[1]) as f:
-        total = process_data(f)
-        print(f"Total middle-sum is {total}")
+        total = sum_correct_middles(f)
+        print(f"Total middle-sum of correct lines is {total}")
+    with open(sys.argv[1]) as f:
+        total = sum_incorrect_middles(f)
+        print(f"Total middle-sum of corrected incorrect lines is {total}")
 
 
 if __name__ == '__main__':

day5/test.py

@@ -1,5 +1,5 @@
 import logging
-from solver import process_data
+from solver import sum_correct_middles, sum_incorrect_middles
 
 logger = logging.getLogger()
 logger.setLevel(logging.DEBUG)
@@ -37,10 +37,14 @@ test_data = r"""
 
 
 def test_main():
-    print("Beginning basic test")
-    result = process_data(iter(test_data.splitlines()))
+    print("Beginning correct middle sum test")
+    result = sum_correct_middles(iter(test_data.splitlines()))
     assert result == 143
-    print("Basic test passed")
+    print("Correct middle sum test passed")
+    print("Beginning incorrect middle sum test")
+    result = sum_incorrect_middles(iter(test_data.splitlines()))
+    assert result == 123
+    print("Incorrect middle sum test passed")
 
 if __name__ == '__main__':
     test_main()