day09: add solutions

Author: tfaughnan

day09/1.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env pypy3
+
+import sys
+
+NUMKNOTS = 2
+DIRECTIONS = {
+    'R': 1,
+    'L': -1,
+    'U': 1j,
+    'D': -1j,
+}
+
+def update(z1, z2):
+    dz = z1 - z2
+    if abs(dz) < 2: # ceil(sqrt(2))
+        return 0
+    return complex(*(part / abs(part) if part else 0
+                     for part in (dz.real, dz.imag)))
+
+def main():
+    knots = [0 + 0j] * NUMKNOTS
+    visited = {knots[-1]}
+    for line in sys.stdin:
+        direction, magnitude = line.split()
+        for _ in range(int(magnitude)):
+            knots[0] += DIRECTIONS[direction]
+            for i in range(1, NUMKNOTS):
+                knots[i] += update(knots[i - 1], knots[i])
+            visited.add(knots[-1])
+
+    print(len(visited))
+
+if __name__ == '__main__':
+    main()

day09/2.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env pypy3
+
+import sys
+
+NUMKNOTS = 10
+DIRECTIONS = {
+    'R': 1,
+    'L': -1,
+    'U': 1j,
+    'D': -1j,
+}
+
+def update(z1, z2):
+    dz = z1 - z2
+    if abs(dz) < 2: # ceil(sqrt(2))
+        return 0
+    return complex(*(part / abs(part) if part else 0
+                     for part in (dz.real, dz.imag)))
+
+def main():
+    knots = [0 + 0j] * NUMKNOTS
+    visited = {knots[-1]}
+    for line in sys.stdin:
+        direction, magnitude = line.split()
+        for _ in range(int(magnitude)):
+            knots[0] += DIRECTIONS[direction]
+            for i in range(1, NUMKNOTS):
+                knots[i] += update(knots[i - 1], knots[i])
+            visited.add(knots[-1])
+
+    print(len(visited))
+
+if __name__ == '__main__':
+    main()