Day 8

2023/day08/code.py

@@ -0,0 +1,51 @@
+#!/usr/bin/env python3
+
+import sys,re
+from math import lcm
+
+
+if __name__ == '__main__':
+    lines = [line.strip('\n') for line in open(sys.argv[1])]
+    lri = list(lines[0])
+    network = {}
+    start = []
+    for line in lines[2:]:
+        groups = re.search(r'(?P<start>.*) = \((?P<left>.*), (?P<right>.*)\)',line)
+        network[groups['start']] = (groups['left'], groups['right'])
+        if groups['start'][2] == 'A': start.append(groups['start'])
+
+    # challenge 1
+    s, e = 'AAA', 'ZZZ'
+    current = s
+    instr = 0
+    while current != e:
+        i = 0 if lri[instr%len(lri)] == 'L' else 1
+        current = network[current][i]
+        instr += 1
+
+    res1 = str(instr)
+    print(f"challenge 1:\n{res1}\n")
+
+    # challenge 2
+    instr = [0] * len(start)
+    ends = []
+    for i in range(len(start)):
+        ends.append([])
+    for a,s in enumerate(start):
+        current = s
+        while True:
+            i = 0 if lri[instr[a]%len(lri)] == 'L' else 1
+            current = network[current][i]
+            instr[a] += 1
+            if current[2] == 'Z':
+                b = False
+                for c,u in ends[a]:
+                    if c == current and (instr[a] % u) == 0:
+                        b = True
+                        break
+                if b: break
+                ends[a].append((current, instr[a]))
+
+    res2 = str(lcm(*[e[0][1] for e in ends]))
+    print(f"challenge 2:\n{res2}\n")
+