09

09/09.py

@@ -0,0 +1,57 @@
+from math import dist
+
+with open('input') as file:
+    cmds = file.read().strip().split('\n')
+
+d = {
+    'R': (0, 1),
+    'L': (0, -1),
+    'U': (1, 0),
+    'D': (-1, 0),
+}
+
+def walk(cmds):
+    for cmd in cmds:
+        cmd, v = cmd.split()
+        v = int(v)
+        cmd = d[cmd]
+        for _ in range(v):
+            yield cmd
+
+def sign(x):
+    if x==0:
+        return 0
+    return x//abs(x)
+
+visited = {(0,0)}
+head = (0,0)
+tail = (0,0)
+for i, j in walk(cmds):
+    hi, hj = head
+    hi += i
+    hj += j
+    head = hi, hj
+    if dist(head, tail)>2**0.5:
+        ti, tj = tail
+        tj += sign(hj-tj)
+        ti += sign(hi-ti)
+        tail = ti, tj
+        visited.add(tail)
+print(len(visited))
+
+rope = [(0,0)]*10
+visited = {(0,0)}
+for i, j in walk(cmds):
+    hi, hj = rope[0]
+    hi += i
+    hj += j
+    rope[0] = hi, hj
+    for i, (head, tail) in enumerate(zip(rope, rope[1:]), 1):
+        if dist(head, tail)>2**0.5:
+            hi, hj = head
+            ti, tj = tail
+            tj += sign(hj-tj)
+            ti += sign(hi-ti)
+            rope[i] = ti, tj
+    visited.add(rope[-1])
+print(len(visited))