From 446affa69f1838bd60ebec3e4da9667e282ef7ea Mon Sep 17 00:00:00 2001
From: Thibaud <thibaud.gasser@gmx.com>
Date: Fri, 8 Dec 2023 14:24:07 +0100
Subject: [PATCH] day 8 part 2

---
 day8/day8.py | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/day8/day8.py b/day8/day8.py
index f2cde82..8c19236 100644
--- a/day8/day8.py
+++ b/day8/day8.py
@@ -1,4 +1,5 @@
 import re
+import math
 from itertools import cycle
 
 def parse_input(infile):
@@ -23,42 +24,42 @@ def part1(directions, nodes):
             current_node = nodes[current_node][0]
         else:
             current_node = nodes[current_node][1]
-    print(f"Reached 'ZZZ' in {iterations} iterations")
+    print(f"Part 1: reached 'ZZZ' in {iterations} iterations")
 
 
 def part2(directions, nodes):
     current_nodes = [k for k in nodes.keys() if k.endswith("A")]
+    # keep track of iterations number for each visited node 
+    # (the number will stop to beeing incremented once the node n_i value reached the target value 'xxZ')
     iterations = [0] * len(current_nodes)
-    print(current_nodes, iterations)
 
     for d in cycle(directions):
         if all(c.endswith("Z") for c in current_nodes):
             break
-        #iterations += len(current_nodes)
+
         if d == "L":
             new_nodes = []
             for i, n in enumerate(current_nodes):
-                if not n.endswith("Z"):
+                if n.endswith("Z"):  # end condition already reached for this node
+                    new_nodes.append(n)
+                else:
                     new_nodes.append(nodes[n][0])
                     iterations[i] += 1
-                else:
-                    new_nodes.append(n)
             current_nodes = new_nodes
-            #current_nodes = [c if c.endswith("Z") else nodes[c][0] for c in current_nodes]
         else:
             new_nodes = []
             for i, n in enumerate(current_nodes):
-                if not n.endswith("Z"):
+                if n.endswith("Z"):  # end condition already reached for this node
+                    new_nodes.append(n)
+                else:
                     new_nodes.append(nodes[n][1])
                     iterations[i] += 1
-                else:
-                    new_nodes.append(n)
             current_nodes = new_nodes
-            #current_nodes = [c if c.endswith("Z") else nodes[c][1] for c in current_nodes]
-        print(current_nodes, iterations)
-        
-    
-    print(f"Reached all nodes such that 'xxZ' in {iterations} iterations")
+
+    # the result is the lowest common multiple between the number of iterations
+    # for each node
+    result = math.lcm(*iterations)
+    print(f"Part 2: reached all nodes such that 'xxZ' in {result} iterations")
 
 
 if __name__ == "__main__":