Add solution for day 5

src/day05.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+
+from math import floor
+from util import read_input
+
+
+def parse_input(lines):
+    updates = []
+    dependencies = {}
+    for line in lines:
+        if "|" in line:
+            (left, right) = line.split('|')
+            if right not in dependencies:
+                dependencies[right] = set()
+            dependencies[right].add(left)
+        elif ',' in line:
+            updates.append(line.split(','))
+    return (dependencies, updates)
+
+
+# Returns the middle page number if the update is correctly ordered, else None
+def find_middle(dependencies, update):
+    for i, page in enumerate(update):
+        page_dependencies = dependencies[page] if page in dependencies else []
+        for dependency in page_dependencies:
+            if dependency in update and update.index(dependency) > i:
+                return None
+    return int(update[floor(len(update) / 2)])
+
+
+# sorts the update so that it's valid and returns its middle page number
+def fix_order(dependencies, update):
+    update = list(update)
+    i = len(update) - 1
+    while i > -1:
+        page = update[i]
+        page_dependencies = dependencies[page] if page in dependencies else []
+        for dependency in page_dependencies:
+            index = update.index(dependency) if dependency in update else -1
+            if index > i:
+                del update[index]
+                update.insert(i, dependency)
+        i -= 1
+    middle = find_middle(dependencies, update)
+    if middle is None:
+        return fix_order(dependencies, update)
+    else:
+        return middle
+
+
+def part1(input_lines):
+    (dependencies, updates) = parse_input(input_lines)
+    total = 0
+    for update in updates:
+        middle = find_middle(dependencies, update)
+        if middle is not None:
+            total += middle
+    return total
+
+
+def part2(input_lines):
+    (dependencies, updates) = parse_input(input_lines)
+    total = 0
+    for update in updates:
+        middle = find_middle(dependencies, update)
+        if middle is None:
+            total += fix_order(dependencies, update)
+    return total
+
+
+test_input = read_input("_test")
+assert 143 == part1(test_input)
+
+real_input = read_input()
+print(part1(real_input))
+
+assert 123 == part2(test_input)
+print(part2(real_input))