From 7a292b026dabe6bea58b7733374475295df56211 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Sat, 23 Jan 2021 17:30:37 +0100
Subject: [PATCH] Implement 2019 day 3

---
 2019/aoc2019/day03.py    | 44 ++++++++++++++++++++++++++++++++++++++++
 2019/tests/test_day03.py | 25 +++++++++++++++++++++++
 2 files changed, 69 insertions(+)
 create mode 100644 2019/aoc2019/day03.py
 create mode 100644 2019/tests/test_day03.py

diff --git a/2019/aoc2019/day03.py b/2019/aoc2019/day03.py
new file mode 100644
index 0000000..9c0c272
--- /dev/null
+++ b/2019/aoc2019/day03.py
@@ -0,0 +1,44 @@
+import itertools
+from typing import Dict, TextIO
+
+
+def compute_points(line: str) -> Dict[complex, int]:
+    points: Dict[complex, int] = {}
+    steps = itertools.count(1)
+
+    pos = complex(0)
+
+    directions = {
+        'U': 1j,
+        'R': 1,
+        'D': -1j,
+        'L': -1,
+    }
+
+    for move in line.strip().split(','):
+        direction = directions[move[0]]
+
+        for _ in range(int(move[1:])):
+            pos += direction
+
+            points.setdefault(pos, next(steps))
+
+    return points
+
+
+def part1(data: TextIO) -> int:
+    points_a = compute_points(next(data))
+    points_b = compute_points(next(data))
+
+    in_common = set(points_a.keys()) & set(points_b.keys())
+
+    return int(min(abs(c.imag) + abs(c.real) for c in in_common))
+
+
+def part2(data: TextIO) -> int:
+    points_a = compute_points(next(data))
+    points_b = compute_points(next(data))
+
+    in_common = set(points_a.keys()) & set(points_b.keys())
+
+    return min(points_a[pos] + points_b[pos] for pos in in_common)
diff --git a/2019/tests/test_day03.py b/2019/tests/test_day03.py
new file mode 100644
index 0000000..7a691ae
--- /dev/null
+++ b/2019/tests/test_day03.py
@@ -0,0 +1,25 @@
+from io import StringIO
+
+import pytest
+
+from aoc2019.day03 import part1, part2
+
+SAMPLES = [
+    "R8,U5,L5,D3\nU7,R6,D4,L4",
+    "R75,D30,R83,U83,L12,D49,R71,U7,L72\nU62,R66,U55,R34,D71,R55,D58,R83",
+    "R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51\nU98,R91,D20,R16,D67,R40,U7,R15,U6,R7",
+]
+
+
+@pytest.mark.parametrize('paths,outcome', zip(SAMPLES, [6, 159, 135]))
+def test_part1(paths: str, outcome: int):
+    path_data = StringIO(paths)
+
+    assert part1(path_data) == outcome
+
+
+@pytest.mark.parametrize('paths,outcome', zip(SAMPLES, [30, 610, 410]))
+def test_part2(paths: str, outcome: int):
+    path_data = StringIO(paths)
+
+    assert part2(path_data) == outcome