Added solution for day 5

day5/example.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

day5/solution.py

@@ -0,0 +1,49 @@
+import sys
+
+def main():
+    lines = sys.stdin.read().splitlines()
+
+    order_rules = set()
+    updates = []
+    i = 0
+    n = len(lines)
+    while i < n and lines[i].strip():
+        line = lines[i].strip()
+        if '|' in line:
+            x, y = line.split('|')
+            x = int(x)
+            y = int(y)
+            order_rules.add((x, y))
+        i += 1
+
+    while i < n and not lines[i].strip():
+        i += 1
+
+    while i < n:
+        line = lines[i].strip()
+        if line:
+            update = [int(x) for x in line.split(',')]
+            updates.append(update)
+        i += 1
+
+    middle_pages = []
+
+    for update in updates:
+        position = {page: idx for idx, page in enumerate(update)}
+        valid = True
+        for x, y in order_rules:
+            if x in position and y in position:
+                if position[x] >= position[y]:
+                    valid = False
+                    break
+
+        if valid:
+            mid_index = len(update) // 2
+            middle_page = update[mid_index]
+            middle_pages.append(middle_page)
+
+    total = sum(middle_pages)
+    print(total)
+
+if __name__ == "__main__":
+    main()

day5/solution2.py

@@ -0,0 +1,83 @@
+import sys
+import collections
+
+def main():
+
+    lines = sys.stdin.read().splitlines()
+
+    order_rules = set()
+    updates = []
+    i = 0
+    n = len(lines)
+    while i < n and lines[i].strip():
+        line = lines[i].strip()
+        if '|' in line:
+            x, y = line.split('|')
+            x = int(x)
+            y = int(y)
+            order_rules.add((x, y))
+        i += 1
+
+    while i < n and not lines[i].strip():
+        i += 1
+
+    while i < n:
+        line = lines[i].strip()
+        if line:
+            update = [int(x) for x in line.split(',')]
+            updates.append(update)
+        i += 1
+
+    middle_pages_correct = []
+    middle_pages_incorrect = []
+
+    for update in updates:
+        position = {page: idx for idx, page in enumerate(update)}
+
+        valid = True
+        for x, y in order_rules:
+            if x in position and y in position:
+                if position[x] >= position[y]:
+                    valid = False
+                    break
+
+        if valid:
+            mid_index = len(update) // 2
+            middle_page = update[mid_index]
+            middle_pages_correct.append(middle_page)
+        else:
+            pages_in_update = set(update)
+            graph = collections.defaultdict(list)
+            indegree = collections.defaultdict(int)
+            for x in pages_in_update:
+                indegree[x] = 0
+
+            for x, y in order_rules:
+                if x in pages_in_update and y in pages_in_update:
+                    graph[x].append(y)
+                    indegree[y] += 1
+
+            queue = collections.deque([node for node in pages_in_update if indegree[node] == 0])
+            sorted_pages = []
+
+            while queue:
+                node = queue.popleft()
+                sorted_pages.append(node)
+                for neighbor in graph[node]:
+                    indegree[neighbor] -= 1
+                    if indegree[neighbor] == 0:
+                        queue.append(neighbor)
+
+            if len(sorted_pages) != len(pages_in_update):
+                print("Cycle detected in ordering rules. Cannot perform topological sort.")
+                sys.exit(1)
+
+            mid_index = len(sorted_pages) // 2
+            middle_page = sorted_pages[mid_index]
+            middle_pages_incorrect.append(middle_page)
+
+    total_incorrect = sum(middle_pages_incorrect)
+    print(total_incorrect)
+
+if __name__ == "__main__":
+    main()