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y2019/p12.py

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+import functools
+import itertools
+import re
+import sys
+from math import gcd
+
+
+def calculate_energy(moons, vels):
+    return sum(
+        sum(abs(p) for p in moon) * sum(abs(v) for v in vel)
+        for moon, vel in zip(moons, vels)
+    )
+
+
+def simulate(text, axes=slice(0, 3), lim=None):
+    g = (int(n) for n in re.findall(r'-?\d+', text))
+    moons = [point[axes] for point in zip(*[g] * 3)]
+    vels = [[0, 0, 0] for m in moons]
+
+    seen = set()
+    for step in itertools.count():
+        if lim is not None and step >= lim:
+            break
+
+        for (i, A), (j, B) in itertools.combinations(enumerate(moons), 2):
+            dV = [max(a < b, 0) or -max(b < a, 0) for a, b in zip(A, B)]
+            vels[i] = [v + d for v, d in zip(vels[i], dV)]
+            vels[j] = [v - d for v, d in zip(vels[j], dV)]
+
+        for i, moon in enumerate(moons):
+            moons[i] = [p + v for p, v in zip(moons[i], vels[i])]
+
+        key = str(moons) + str(vels)
+        if key in seen:
+            break
+        seen.add(key)
+
+    return step, calculate_energy(moons, vels)
+
+
+text = sys.stdin.read()
+
+_, energy = simulate(text, lim=1000)
+print(energy)
+
+nX, _ = simulate(text, axes=slice(0, 1))
+nY, _ = simulate(text, axes=slice(1, 2))
+nZ, _ = simulate(text, axes=slice(2, 3))
+gcds = {gcd(p, q) for p, q in itertools.combinations([nX, nY, nZ], 2)}
+lcm = functools.reduce(int.__mul__, gcds)
+print(nX * nY * nZ // lcm)