Advent of Code 2024 - Day 5 : Python version

advent_of_code/2024(python)/day5.py

@@ -0,0 +1,30 @@
+
+from collections import defaultdict
+
+def solve_day5_part1(rules:list[str], pages:list[str])->int:
+    before_rules = defaultdict(list)
+    for rule in rules:
+        first, second = rule.split("|")
+        # each item stores what item must be before current one
+        # before the rule : 75 : [97]
+        # after the rule :  97 : [75]
+        before_rules[int(second)].append(int(first))
+
+    res = 0
+    for page in pages:
+        nums = [int(num) for num in page.split(",")]
+        is_ok = True
+        for i in range(1, len(nums)):
+            for j in range(i):
+                # check whether it fits with the rule
+                first_num, second_num = nums[j], nums[i]
+                if second_num in before_rules[first_num]:
+                    is_ok = False
+                    break
+            if not is_ok:
+                break
+
+        if is_ok:
+            res += nums[len(nums)//2-1 if len(nums)%2==0 else len(nums)//2]
+
+    return res