Solve 2020 day 13 CRT jojo

2020/d13.py

@@ -0,0 +1,39 @@
+from lib import get_data, str_to_ints, mod_inverse
+from functools import reduce
+
+data = get_data(__file__)
+lines = data.splitlines()
+
+earliest = int(lines[0])
+times = str_to_ints(lines[1])
+
+mintime = 10**21
+id = None
+
+for time in times:
+    mintimecur = (earliest // time) * time + time
+    if mintimecur < mintime:
+        mintime = mintimecur
+        id = time
+
+
+assert id is not None
+print((mintime - earliest) * id)
+
+fields = lines[1].split(",")
+
+buses = []
+for offset, busid in enumerate(fields):
+    if busid == "x":
+        continue
+    period = int(busid)
+    buses.append((period, -offset % period))
+
+
+total = 0
+product = reduce(lambda a, b: a * b, map(lambda x: x[0], buses))
+for period, offset in buses:
+    p = product // period
+    total += offset * mod_inverse(p, period) * p
+
+print(total % product)