Day 13 (cleanup)

day13/part2.py

@@ -14,12 +14,11 @@ def merge(a, b, x, y):
             b += a * ((y-b-1) // a + 1)
         else:
             y += x * ((b-y-1) // x + 1)
-    d = b
-    c = lcm(a, x)
-    return c, d
+    return lcm(a, x), b
 
 
 lines = [x.strip() for x in open("input.txt")]
+# f(n) = [interval] * n + [offset]  -->  (interval, offset)
 busses = ((int(x), -idx) for idx, x in enumerate(lines[1].split(',')) if x != 'x')
 sequence = reduce(lambda fn, fm: merge(*fn, *fm), busses, (1, 0))
 print(sequence[1])