From 52fba3b92f93f769d1810989582917575fa0d6f6 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Sat, 12 Dec 2020 10:06:19 +0100
Subject: [PATCH] 2020: d12: ex2: add solution

---
 2020/d12/ex2/ex2.py | 69 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100755 2020/d12/ex2/ex2.py

diff --git a/2020/d12/ex2/ex2.py b/2020/d12/ex2/ex2.py
new file mode 100755
index 0000000..90d5f87
--- /dev/null
+++ b/2020/d12/ex2/ex2.py
@@ -0,0 +1,69 @@
+#!/usr/bin/env python
+
+import sys
+from dataclasses import dataclass
+from typing import List, Tuple
+
+Instruction = Tuple[str, int]
+Position = Tuple[int, int]
+
+
+@dataclass
+class Ship:
+    pos: Position
+    rel_waypoint: Position
+
+
+ORIENTATIONS = ["N", "W", "S", "E"]
+MOVES = {
+    "N": (1, 0),
+    "W": (0, -1),
+    "S": (-1, 0),
+    "E": (0, 1),
+}
+
+
+def move_ship(pos: Ship, instr: Instruction) -> Ship:
+    if instr[0] == "L":
+        assert instr[1] % 90 == 0
+        turns = instr[1] // 90
+        x, y = pos.rel_waypoint
+        for __ in range(turns):
+            x, y = y, -x
+        return Ship(pos.pos, (x, y))
+    elif instr[0] == "R":
+        assert instr[1] % 90 == 0
+        turns = instr[1] // 90
+        x, y = pos.rel_waypoint
+        for __ in range(turns):
+            x, y = -y, x
+        return Ship(pos.pos, (x, y))
+    elif instr[0] == "F":
+        dx, dy = pos.rel_waypoint
+        x, y = pos.pos
+        x += dx * instr[1]
+        y += dy * instr[1]
+        return Ship((x, y), pos.rel_waypoint)
+    else:
+        dx, dy = MOVES[instr[0]]
+        x, y = pos.rel_waypoint
+        x += dx * instr[1]
+        y += dy * instr[1]
+        return Ship(pos.pos, (x, y))
+
+
+def solve(raw: List[str]) -> int:
+    instructions = [(i[0], int(i[1:])) for i in raw]
+    ship = Ship((0, 0), (1, 10))
+    for i in instructions:
+        ship = move_ship(ship, i)
+    return sum(abs(c) for c in ship.pos)
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()