Solve 2023:08 "Haunted Wasteland"

Part 2 would have taken 10-15 hours with brute force.

After I figured out the puzzle input had circular
A-Z paths, it was plain as day that LCM was the
solution to the problem.

https://en.wikipedia.org/wiki/Least_common_multiple

2023-python/output/day_08.py

@@ -0,0 +1,65 @@
+import re
+from math import lcm
+from output import answer, puzzleinput
+
+n = 8
+title = "Haunted Wasteland"
+
+
+@answer(1, "One can reach Z in {} steps")
+def part_1(presolved):
+    steps, _ = presolved
+    return steps
+
+
+@answer(2, "Ghost path takes {} steps before all ghosts are at a Z positon")
+def part_2(presolved):
+    _, ghost_meet_point = presolved
+    return ghost_meet_point
+
+
+@puzzleinput(n)
+def parse_input(data):
+    return data
+
+
+def presolve(data):
+    d, els = data.split("\n\n")
+    r = len(d)
+    e = dict()
+    for el in els.splitlines():
+        k, *lr = re.match(r"(\w+) = \((\w+), (\w+)\)", el).groups()
+        e[k] = lr
+
+    p1 = 0
+    pos = "AAA"
+    while pos != "ZZZ":
+        i = 0 if d[p1 % r] == "L" else 1
+        pos = e[pos][i]
+        p1 += 1
+
+    p2 = 0
+    z = list()
+    for spos in [p for p in e.keys() if p.endswith("A")]:
+        s = 0
+        pos = spos
+        while not pos.endswith("Z"):
+            i = 0 if d[s % r] == "L" else 1
+            pos = e[pos][i]
+            s += 1
+        z.append(s)
+    p2 = lcm(*z)
+
+    return p1, p2
+
+
+if __name__ == "__main__":
+    inp = parse_input()
+
+    inp = presolve(inp)
+
+    a = part_1(inp)
+    b = part_2(inp)
+
+    assert a == 17141
+    assert b == 10818234074807