From f5c1b03ddd79af35f1dfa7c163226518a7b1abf5 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <bruno@belanyi.fr>
Date: Thu, 24 Dec 2020 13:26:37 +0100
Subject: [PATCH] 2020: d24: ex1: add solution

---
 2020/d24/ex1/ex1.py | 49 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100755 2020/d24/ex1/ex1.py

diff --git a/2020/d24/ex1/ex1.py b/2020/d24/ex1/ex1.py
new file mode 100755
index 0000000..8c6d8ac
--- /dev/null
+++ b/2020/d24/ex1/ex1.py
@@ -0,0 +1,49 @@
+#!/usr/bin/env python
+
+import sys
+from collections import defaultdict
+from typing import Dict, List, Tuple
+
+Offset = Tuple[int, int]
+
+DELTAS = {
+    "nw": (0, -1),
+    "ne": (1, -1),
+    "e": (1, 0),
+    "se": (0, 1),
+    "sw": (-1, 1),
+    "w": (-1, 0),
+}
+
+
+def to_offset(path: str) -> Offset:
+    offset = 0, 0
+    i = 0
+    while i < len(path):
+        direction = path[i]
+        i += 1
+        if direction in ["s", "n"]:
+            direction += path[i]
+            i += 1
+        x, y = offset
+        dx, dy = DELTAS[direction]
+        offset = x + dx, y + dy
+    return offset
+
+
+def solve(raw: List[str]) -> int:
+    blacks: Dict[Offset, bool] = defaultdict(bool)
+
+    for offset in map(to_offset, raw):
+        blacks[offset] = not blacks[offset]
+
+    return sum(blacks.values())
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()