day03 finished

advent/days/day03/solution.py

@@ -0,0 +1,55 @@
+from __future__ import annotations
+
+from typing import Iterator
+
+day_num = 3
+
+
+def part1(lines: Iterator[str]) -> int:
+    return sum(Rucksack.find_double(line) for line in lines)
+
+
+def part2(lines: Iterator[str]) -> int:
+    groups = [lines] * 3
+    zipped = zip(*groups, strict=True)
+    return sum(Rucksack.find_common(group) for group in zipped)
+
+
+class Rucksack:
+    @staticmethod
+    def priority(char: str) -> int:
+        """
+        Returns the priority given to each item.
+        It is assumed, that we are given a valid item
+        """
+        num = ord(char)
+        if ord('a') <= num and num <= ord('z'):
+            return num - ord('a') + 1
+        if ord('A') <= num and num <= ord('Z'):
+            return num - ord('A') + 27
+        raise Exception(f"Unknown char: {char}")
+
+    @staticmethod
+    def find_double(rucksack: str) -> int:
+        """
+        Finds the priority of the one item in both compartments.
+        It is assumed that there is only one such item
+        """
+        half = len(rucksack) // 2
+        first = rucksack[:half]
+        second = rucksack[half:]
+        for item in first:
+            if item in second:
+                return Rucksack.priority(item)
+        raise Exception("No double item")
+
+    @staticmethod
+    def find_common(group: tuple[str, ...]) -> int:
+        """
+        Finds the one item in all three rucksacks given.
+        It is assumed that there is only one such item and group has exactly three rucksacks
+        """
+        for item in group[0]:
+            if item in group[1] and item in group[2]:
+                return Rucksack.priority(item)
+        raise Exception("No common item found")