finished day 12b

days/test_day12.py

@@ -1,6 +1,9 @@
-from itertools import permutations
 import os
 import re
+from copy import deepcopy
+from functools import reduce
+from itertools import permutations
+from math import gcd
 
 inputfile = os.path.join(os.path.dirname(__file__), "input/day12_input")
 
@@ -32,3 +35,28 @@ def test_day12a():
         e += (abs(p[0])+abs(p[1])+abs(p[2]))*(abs(v[0])+abs(v[1])+abs(v[2]))
 
     assert e == 9139
+
+
+def test_day12b():
+    """
+    Finished with helpful hints from ZuBsPaCe
+    https://www.reddit.com/r/adventofcode/comments/e9jxh2/help_2019_day_12_part_2_what_am_i_not_seeing/far9cgu/
+    """
+    moons = [[m, [0, 0, 0]] for m in get_moons()]
+    com = []
+    for i in range(3):
+        count = 0
+        initial = deepcopy(moons)
+        while True:
+            for me, other in permutations(moons, 2):
+                pa = me[0]
+                pb = other[0]
+                me[1][i] += -1 if pa[i] > pb[i] else 1 if pa[i] < pb[i] else 0
+            for moon in moons:
+                moon[0][i] += moon[1][i]
+            count += 1
+            if moons == initial:
+                break
+        com.append(count)
+    steps = reduce(lambda a, b: int(a * b / gcd(a, b)), com)
+    assert steps == 420788524631496