day 20 finished

advent/days/day20/data/example01.txt

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+1
+2
+-3
+3
+-2
+0
+4

advent/days/day20/solution.py

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+from __future__ import annotations
+from dataclasses import dataclass
+
+from typing import Iterable, Iterator, Self
+
+day_num = 20
+
+
+def part1(lines: Iterator[str]) -> int:
+    ring = Ring.create(int(line) for line in lines)
+    ring.process(1)
+    return sum(ring.get_ordered([1000, 2000, 3000]))
+
+
+def part2(lines: Iterator[str]) -> int:
+    ring = Ring.create(int(line) * 811589153 for line in lines)
+    ring.process(10)
+    return sum(ring.get_ordered([1000, 2000, 3000]))
+
+
+@dataclass(slots=True)
+class Ring:
+    """ Datastructure that stores Items in a Ring """
+    items: list[RingItem]
+
+    @classmethod
+    def create(cls, values: Iterable[int]):
+        """ Crates ring from an Iterable """
+        value_iterator = iter(values)
+
+        current = RingItem.create(next(value_iterator))
+        items = [current]
+        for value in value_iterator:
+            current = current.append(value)
+            items.append(current)
+
+        return Ring(items)
+
+    @property
+    def zero(self) -> RingItem:
+        """ Helper to find the first item with value zero. Raises Exception if there is none. """
+        for item in self.items:
+            if item.value == 0:
+                return item
+        raise Exception("No Zero Item found")
+
+    def process(self, rounds: int):
+        """ Processes the given number of complete rounds. """
+        for _ in range(rounds):
+            for item in self.items:
+                item.move(len(self.items))
+
+    def get_ordered(self, values: list[int]) -> Iterator[int]:
+        """ Returns the values at the given ordered positions """
+        for n, item in zip(range(max(values) + 1), self.zero):
+            if n in values:
+                yield item
+
+
+@dataclass(slots=True)
+class RingItem:
+    """ A class to store one Item in a Ring"""
+    value: int
+    next: RingItem
+    prev: RingItem
+
+    @classmethod
+    def create(cls, value: int) -> Self:
+        """ Creates a single Ring Element that points to itself"""
+        root = RingItem(value, None, None)  # type: ignore
+        root.next = root
+        root.prev = root
+        return root
+
+    def append(self, value: int) -> RingItem:
+        """ Appends the given value to the current element """
+        next = RingItem(value, self.next, self)
+        self.next.prev = next
+        self.next = next
+        return next
+
+    def move(self, item_count: int):
+        """  Moves the current element according to its value """
+        steps = self.value % (item_count - 1)
+
+        if steps == 0:
+            return
+
+        self.next.prev = self.prev
+        self.prev.next = self.next
+
+        new_pos = self
+        for _ in range(steps):
+            new_pos = new_pos.next
+
+        self.prev = new_pos
+        self.next = new_pos.next
+
+        new_pos.next.prev = self
+        new_pos.next = self
+
+    def __iter__(self) -> Iterator[int]:
+        """ Never ending iterator through items"""
+        current = self
+        while True:
+            yield current.value
+            current = current.next
+
+    def stopping(self) -> Iterator[int]:
+        """ Iterator that iterates exactly once through all items """
+        current = self
+        while True:
+            yield current.value
+            current = current.next
+            if current == self:
+                break

advent/days/day20/test_solution.py

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+from advent.common import input
+
+from .solution import Ring, day_num, part1, part2
+
+
+def test_part1():
+    lines = input.read_lines(day_num, 'example01.txt')
+    expected = 3
+    result = part1(lines)
+    assert result == expected
+
+
+def test_part2():
+    lines = input.read_lines(day_num, 'example01.txt')
+    expected = 1623178306
+    result = part2(lines)
+    assert result == expected
+
+
+def test_once():
+    lines = (int(line) for line in input.read_lines(day_num, 'example01.txt'))
+    ring = Ring.create(lines)
+    ring.process(1)
+
+    expected = [0, 3, -2, 1, 2, -3, 4]
+    assert list(ring.zero.stopping()) == expected
+
+
+def test_get_odered():
+    lines = (int(line) for line in input.read_lines(day_num, 'example01.txt'))
+    ring = Ring.create(lines)
+    ring.process(1)
+
+    expected = [4, -3, 2]
+    assert list(ring.get_ordered([1000, 2000, 3000])) == expected