Test files

toolkit.py

@@ -16,10 +16,6 @@ from pathlib import Path
 product = functools.partial(functools.reduce, operator.mul)
 
 
-def lcm(a, b):
-    return abs(a * b) // math.gcd(a, b)
-
-
 def render(grid, brush=None):
     if brush is None:
         brush = {v: v for v in grid.values()}

y2023/p05.py

@@ -26,9 +26,10 @@ print(ans2)
 
 # old method, slow
 def backward(n):
-    for group in groups:
+    for group in groups[::-1]:
         n = next((n - (b - a) for b, a, c in group if b <= n < b + c), n)
     return n
 
+
 pairs = [(a, a + b) for a, b in zip(seed[::2], seed[1::2])]
-next(n for n in itertools.count(ans2) if any(a <= backward(n) < a + b for a, b in pairs))
+next(n for n in itertools.count(ans2) if any(a <= backward(n) < b for a, b in pairs))

y2023/p08.py

@@ -0,0 +1,31 @@
+import math
+import collections
+import itertools
+import re
+
+
+text = open(0).read()
+head, tail = text.split('\n\n')
+mapping = {}
+for line in tail.splitlines():
+    aa, bb, cc = re.findall(r'[\dA-Z]{3}', line)
+    mapping[aa] = [bb, cc]
+
+pos = 'AAA'
+steps = itertools.cycle(map('LR'.index, head))
+for ans1 in itertools.count(1):
+    pos = mapping[pos][next(steps)]
+    if pos == 'ZZZ':
+        break
+print(ans1)
+
+state = [p for p in mapping if p.endswith('A')]
+seen = collections.defaultdict(collections.Counter)
+steps = itertools.cycle(enumerate(map('LR'.index, head)))
+for _ in range(100_000):
+    i, step = next(steps)
+    state = [mapping[pos][step] for pos in state]
+    for j, pos in enumerate(state):
+        seen[j][i, pos] += 1
+ns = [sum(v > 1 for v in c.values()) for c in seen.values()]
+print(math.lcm(*ns))