Solve 2019 day 12

2019/12_jupiter.py

@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+from itertools import chain, combinations, islice
+from math import gcd
+
+def cmp(a, b):
+    return (a > b) - (a < b)
+
+def abssum(i):
+    return sum(map(abs, i))
+
+def lcm(a, b):
+    return abs(a * b) // gcd(a, b)
+
+def sim(axis):
+    pos = list(axis)
+    vel = [0] * len(pos)
+    index_pairs = tuple(combinations(range(len(pos)), 2))
+    while True:
+        for i, j in index_pairs:
+            diff = cmp(pos[j], pos[i])
+            vel[i] += diff
+            vel[j] -= diff
+        for i, v in enumerate(vel):
+            pos[i] += v
+        yield pos, vel
+
+def energy_after(moons, steps):
+    x, y, z = zip(*moons)
+    axes = next(islice(zip(sim(x), sim(y), sim(z)), steps - 1, steps))
+    pos, vel = (tuple(zip(*i)) for i in zip(*axes))
+    return sum(abssum(p) * abssum(v) for p, v in zip(pos, vel))
+
+def axis_cycle(axis):
+    seen = {}
+    for step, (pos, vel) in enumerate(sim(axis)):
+        ident = tuple(chain(pos, vel))
+        if ident in seen:
+            return step - seen[ident]
+        seen[ident] = step
+
+def find_cycle(moons):
+    x, y, z = zip(*moons)
+    return lcm(lcm(axis_cycle(x), axis_cycle(y)), axis_cycle(z))
+
+moons = [(3, 15, 8), (5, -1, -2), (-10, 8, 2), (8, 4, -5)]
+print(energy_after(moons, 1000))
+print(find_cycle(moons))

2019/input/12

@@ -0,0 +1,4 @@
+<x=-1, y=0, z=2>
+<x=2, y=-10, z=-7>
+<x=4, y=-8, z=8>
+<x=3, y=5, z=-1>