From abc742e2ad8fc53b7ef5166ae0a41a89458966e9 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Sat, 3 Jul 2021 14:15:11 +0200
Subject: [PATCH] Implement day 22 part 1

---
 2019/aoc2019/day22.py    | 44 ++++++++++++++++++++++++++++++++++++++++
 2019/tests/test_day22.py | 43 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100644 2019/aoc2019/day22.py
 create mode 100644 2019/tests/test_day22.py

diff --git a/2019/aoc2019/day22.py b/2019/aoc2019/day22.py
new file mode 100644
index 0000000..fc54e39
--- /dev/null
+++ b/2019/aoc2019/day22.py
@@ -0,0 +1,44 @@
+from typing import List, TextIO
+
+
+def shuffle(instructions: List[str], deck_size: int) -> List[int]:
+    deck = list(range(0, deck_size))
+
+    for instruction in instructions:
+        if "new stack" in instruction:
+            deck = list(reversed(deck))
+            continue
+
+        parts = instruction.split(" ")
+        if parts[0] == "cut":
+            by = int(parts[1])
+
+            new_deck = deck[by:]
+            new_deck += deck[:by]
+
+            deck = new_deck
+        else:
+            increment = int(parts[3])
+
+            new_deck = list(range(0, deck_size))
+            target_index = 0
+
+            for card in deck:
+                new_deck[target_index] = card
+                target_index = (target_index + increment) % len(deck)
+
+            deck = new_deck
+
+    return deck
+
+
+def part1(data: TextIO):
+    instructions = [line.strip() for line in data]
+
+    result = shuffle(instructions, 10007)
+
+    for i, card in enumerate(result):
+        if card == 2019:
+            return i
+
+    raise Exception("Did not find card")
diff --git a/2019/tests/test_day22.py b/2019/tests/test_day22.py
new file mode 100644
index 0000000..78866a7
--- /dev/null
+++ b/2019/tests/test_day22.py
@@ -0,0 +1,43 @@
+import pytest
+
+from aoc2019.day22 import shuffle
+
+SAMPLE_INSTRUCTIONS = [
+    """deal with increment 7
+    deal into new stack
+    deal into new stack""",
+    """cut 6
+    deal with increment 7
+    deal into new stack""",
+    """deal with increment 7
+    deal with increment 9
+    cut -2""",
+    """deal into new stack
+    cut -2
+    deal with increment 7
+    cut 8
+    cut -4
+    deal with increment 7
+    cut 3
+    deal with increment 9
+    deal with increment 3
+    cut -1""",
+]
+
+CORRECT_SHUFFLES = [
+    "0 3 6 9 2 5 8 1 4 7",
+    "3 0 7 4 1 8 5 2 9 6",
+    "6 3 0 7 4 1 8 5 2 9",
+    "9 2 5 8 1 4 7 0 3 6",
+]
+
+
+@pytest.mark.parametrize('instructions,correct', zip(SAMPLE_INSTRUCTIONS, CORRECT_SHUFFLES))
+def test_shuffle(instructions, correct):
+    instructions = [line.strip() for line in instructions.splitlines()]
+
+    correct = [int(i) for i in correct.split(" ")]
+
+    result = shuffle(instructions, 10)
+
+    assert result == correct