From 2d561eab7d534f2b597f560d796e04dbc82b0ca6 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Tue, 2 Feb 2021 19:12:10 +0100
Subject: [PATCH] Implement 2019 day 16 part 1

---
 2019/aoc2019/day16.py | 33 +++++++++++++++++++++++++++++++++
 2019/tests/day16.py   | 15 +++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 2019/aoc2019/day16.py
 create mode 100644 2019/tests/day16.py

diff --git a/2019/aoc2019/day16.py b/2019/aoc2019/day16.py
new file mode 100644
index 0000000..217fe68
--- /dev/null
+++ b/2019/aoc2019/day16.py
@@ -0,0 +1,33 @@
+import math
+from typing import List, TextIO
+
+import numpy  # type: ignore
+
+
+def read_input(data: TextIO) -> List[int]:
+    line = next(data).strip()
+
+    return [int(c) for c in line]
+
+
+def simulate(numbers: List[int]) -> str:
+    numbers = numpy.array(numbers)
+    pattern = numpy.array([0, 1, 0, -1], dtype=numpy.int)
+
+    matrix = numpy.zeros((len(numbers), len(numbers)), dtype=numpy.int)
+
+    for i in range(len(numbers)):
+        base = numpy.repeat(pattern, i + 1)
+        needed_repetitions = math.ceil((len(numbers) + 1) / len(base))
+        matrix[i, :] = numpy.tile(base, needed_repetitions)[1:len(numbers) + 1]
+
+    for _ in range(100):
+        numbers = numpy.abs(numpy.dot(matrix, numbers)) % 10
+
+    return ''.join(str(s) for s in numbers[:8])
+
+
+def part1(data: TextIO) -> str:
+    numbers = read_input(data)
+
+    return simulate(numbers)
diff --git a/2019/tests/day16.py b/2019/tests/day16.py
new file mode 100644
index 0000000..f83024d
--- /dev/null
+++ b/2019/tests/day16.py
@@ -0,0 +1,15 @@
+import pytest
+
+from aoc2019.day16 import simulate
+
+
+@pytest.mark.parametrize('data,correct', [
+    ('80871224585914546619083218645595', '24176176'),
+    ('19617804207202209144916044189917', '73745418'),
+    ('69317163492948606335995924319873', '52432133'),
+])
+def test_sample_part1(data: str, correct: str):
+    numbers = [int(c) for c in data]
+
+    assert simulate(numbers) == correct
+    pass