From 9fa6e8ed50c605b58b13b834190b58acf060ef10 Mon Sep 17 00:00:00 2001
From: Drew Winstel <drew@hsv.beer>
Date: Wed, 23 Dec 2020 09:00:00 -0600
Subject: [PATCH] Add Drew's Day 23 solution

I switched from a deque to a linked list for part 2 because the
deque implementation just didn't work for that many turns and that
big of a list.
---
 Drew/drew_day23.py | 111 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 Drew/drew_day23.py

diff --git a/Drew/drew_day23.py b/Drew/drew_day23.py
new file mode 100644
index 0000000..4d5a950
--- /dev/null
+++ b/Drew/drew_day23.py
@@ -0,0 +1,111 @@
+from collections import deque
+from typing import Deque, List
+
+
+TEST_INPUT = [int(i) for i in "389125467"]
+REAL_INPUT = [int(i) for i in "318946572"]
+
+
+def take_turn(cups: Deque[int]):
+    max_cup = len(cups)
+    current_cup = cups[0]
+    cups.rotate(-1)
+    drawn_cups = [cups.popleft() for _ in range(3)]
+    destination = current_cup - 1
+    if destination == 0:
+        destination = max_cup
+    while destination in drawn_cups:
+        destination = destination - 1
+        if destination == 0:
+            destination = max_cup
+    dest_index = cups.index(destination)
+    cups.rotate(0 - dest_index - 1)
+    for i in reversed(drawn_cups):
+        cups.appendleft(i)
+    new_target = cups.index(current_cup)
+    cups.rotate(-new_target - 1)
+
+
+def part_one(puzzle: List[int]) -> str:
+    hand = deque(puzzle)
+    for _ in range(100):
+        take_turn(hand)
+    finished = list(hand)
+    start_index = finished.index(1)
+    result = finished[start_index + 1 :] + finished[:start_index]
+    return "".join(str(i) for i in result)
+
+
+class Cup:
+    def __init__(self, number: int) -> None:
+        self.number = number
+        self.next: Cup = None
+
+    def __repr__(self):
+        return str(self.number)
+
+
+def part_two(puzzle: List[int]) -> int:
+    cups: Dict[int, Cup] = {}
+    for cup_number in puzzle:
+        cups[cup_number] = Cup(cup_number)
+    # tack on the extra numbers
+    for cup_number in range(max(puzzle) + 1, int(1e6 + 1)):
+        cups[cup_number] = Cup(cup_number)
+    # build our relationships to the next one in the list
+    for first, second in zip(puzzle, puzzle[1:] + [10]):
+        cups[first].next = cups[second]
+    # then tack on the rest
+    for cup_number in range(10, 1000000):
+        cups[cup_number].next = cups[cup_number + 1]
+    # and finish the loop
+    cups[1000000].next = cups[puzzle[0]]
+    # coherence check
+    for cup in cups.values():
+        assert cup.next is not None, cup.number
+    # and let us begin
+    current_cup = cups[puzzle[0]]
+    for turn in range(10000000):
+        # draw 3
+        removed_ids = [
+            current_cup.next.number,
+            current_cup.next.next.number,
+            current_cup.next.next.next.number,
+        ]
+        # skip the three cups we've already pulled
+        current_cup.next = current_cup.next.next.next.next
+        destination_cup_id = current_cup.number - 1
+        if destination_cup_id == 0:
+            destination_cup_id = 1000000
+        while destination_cup_id in removed_ids:
+            destination_cup_id -= 1
+            if destination_cup_id == 0:
+                destination_cup_id = 1000000
+
+        destination_cup = cups[destination_cup_id]
+        # place the new ones
+        cups[removed_ids[2]].next = destination_cup.next
+        destination_cup.next = cups[removed_ids[0]]
+        # and advance the turn
+        current_cup = current_cup.next
+    # done!
+    return cups[1].next.number * cups[1].next.next.number
+
+
+def main():
+    test_hand = deque(TEST_INPUT)
+    take_turn(test_hand)
+    assert list(test_hand) == [2, 8, 9, 1, 5, 4, 6, 7, 3], test_hand
+    take_turn(test_hand)
+    assert list(test_hand) == [5, 4, 6, 7, 8, 9, 1, 3, 2], test_hand
+    take_turn(test_hand)
+    assert list(test_hand) == [8, 9, 1, 3, 4, 6, 7, 2, 5], test_hand
+    test_result = part_one(TEST_INPUT)
+    assert test_result == "67384529"
+    print(part_one(REAL_INPUT))
+    assert part_two(TEST_INPUT) == 149245887792
+    print(part_two(REAL_INPUT))
+
+
+if __name__ == "__main__":
+    main()