From f633e19cea33fb600f84aa40862288702b9ac25c Mon Sep 17 00:00:00 2001
From: Gabriel Augendre <gabriel@augendre.info>
Date: Thu, 5 Mar 2020 21:48:44 +0100
Subject: [PATCH] Implement day 6 part 2

---
 2019/day06-orbits.py  | 36 ++++++++++++++++++++++++++++--------
 2019/inputs/day06-ex2 | 13 +++++++++++++
 2 files changed, 41 insertions(+), 8 deletions(-)
 create mode 100644 2019/inputs/day06-ex2

diff --git a/2019/day06-orbits.py b/2019/day06-orbits.py
index 15f818b..cbe0b27 100644
--- a/2019/day06-orbits.py
+++ b/2019/day06-orbits.py
@@ -1,5 +1,5 @@
 from dataclasses import dataclass
-from typing import Dict
+from typing import Dict, List
 
 
 @dataclass
@@ -11,17 +11,38 @@ class Node:
         return self.name.lower() == "com"
 
     def count_hops(self):
-        counter = 0
+        return len(self.chain()) - 1  # Not counting self but it's part of the chain
+
+    def chain(self):
+        chain = [self]
         current = self
         while not current.is_origin():
             current = current.orbits_over
-            counter += 1
-        return counter
+            chain.append(current)
+        return chain
+
+    def common_chain(self, other: "Node") -> List["Node"]:
+        chain = []
+        for el1, el2 in zip(reversed(self.chain()), reversed(other.chain())):
+            if el1 != el2:
+                break
+            chain.append(el1)
+        return chain
+
+    def __str__(self) -> str:
+        if self.orbits_over:
+            return f"{self.orbits_over.name}){self.name}"
+        else:
+            return self.name
+
+    def __eq__(self, other: "Node") -> bool:
+        return self.name == other.name
 
 
 def main():
     with open("inputs/day06") as f:
         orbits = f.read().split()
+
     objects = dict()  # type: Dict[str, Node]
     for orbit in orbits:
         stator, rotor = orbit.split(")")
@@ -31,11 +52,10 @@ def main():
         objects[stator.name] = stator
         objects[rotor.name] = rotor
 
-    counter = 0
-    for obj in objects.values():
-        counter += obj.count_hops()
+    me = objects["YOU"]
+    santa = objects["SAN"]
 
-    print(counter)
+    print(me.count_hops() + santa.count_hops() - 2 * len(me.common_chain(santa)))
 
 
 if __name__ == "__main__":
diff --git a/2019/inputs/day06-ex2 b/2019/inputs/day06-ex2
new file mode 100644
index 0000000..a1007c6
--- /dev/null
+++ b/2019/inputs/day06-ex2
@@ -0,0 +1,13 @@
+COM)B
+B)C
+C)D
+D)E
+E)F
+B)G
+G)H
+D)I
+E)J
+J)K
+K)L
+K)YOU
+I)SAN