From 657fe956f9079ff99bfc7c1777d7b8e76cc5bd3c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anders=20Engl=C3=B6f=20Ytterstr=C3=B6m?= <yttan@fastmail.se>
Date: Thu, 27 Nov 2025 22:36:09 +0100
Subject: [PATCH] Solve 2022 day 9 pt 1-2

Pt 1 was just head and tail. For pt 2 I rewrote the
code to instead build the rope (snake) from head to
tail by always moving the head first and traverse
the body of the snake.

Yes, I think of it as a body of a snake - not knots
on a rope. Child hood memories are to damn colorful
:)

For reference, this is my visually debugging code:

def dbg(seen, snake):
    print(snake)
    for r in range(-4, 1):
        print("".join([v(r, c, snake) for c in range(0, 7)]))
    print("")

def v(r, c, snake):
    if (r,c) == snake[0]:
        return "H"
    for i, n in enumerate(snake[1:-1], start=1):
        if (r,c) == n:
            return str(i)
    if (r,c) == snake[-1]:
        return "T"
    if (r,c) == (0,0):
        return "s"
    return "."
---
 2022-python/output/day_09.py | 71 ++++++++++++++++++++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 2022-python/output/day_09.py

diff --git a/2022-python/output/day_09.py b/2022-python/output/day_09.py
new file mode 100644
index 0000000..2c1e2b7
--- /dev/null
+++ b/2022-python/output/day_09.py
@@ -0,0 +1,71 @@
+from output import DD, ints
+
+
+def solve(data):
+    p12 = []
+    for sl in [2, 10]:
+        seen = set([(0, 0)])
+        snake = [(0, 0)] * sl
+        for line in data.splitlines():
+            d = line[0]
+            for i in range(ints(line)[0]):
+                ns = []
+                hd, *tls = snake
+                r, c = hd
+                hd = r + DD[d][0], c + DD[d][1]
+                ns.append(hd)
+                for tl in tls:
+                    r, c = tl
+                    match (r - hd[0], c - hd[1]):
+                        case (2, -1):
+                            tl = r - 1, c + 1
+                        case (-2, -1):
+                            tl = r + 1, c + 1
+                        case (-2, 1):
+                            tl = r + 1, c - 1
+                        case (2, 1):
+                            tl = r - 1, c - 1
+                        case (1, 2):
+                            tl = r - 1, c - 1
+                        case (-1, 2):
+                            tl = r + 1, c - 1
+                        case (-1, -2):
+                            tl = r + 1, c + 1
+                        case (1, -2):
+                            tl = r - 1, c + 1
+                        case (0, 2):
+                            tl = r, c - 1
+                        case (0, -2):
+                            tl = r, c + 1
+                        case (2, 0):
+                            tl = r - 1, c
+                        case (-2, 0):
+                            tl = r + 1, c
+                        case (2, -2):
+                            tl = r - 1, c + 1
+                        case (-2, -2):
+                            tl = r + 1, c + 1
+                        case (-2, 2):
+                            tl = r + 1, c - 1
+                        case (2, 2):
+                            tl = r - 1, c - 1
+                    ns.append(tl)
+                    hd = tl
+                snake = ns
+                seen.add(tl)
+        p12.append(len(seen))
+    p1, p2 = p12
+    return p1, p2
+
+
+if __name__ == "__main__":
+    with open("./input/09.txt", "r") as f:
+        inp = f.read().strip()
+
+    p1, p2 = solve(inp)
+
+    print(p1)
+    print(p2)
+
+    assert p1 == 6212
+    assert p2 == 2522