Water - Kareha

lib/possible_bipartition.rb

@@ -1,4 +1,40 @@
+# goal - start with first dog, assign it's disliked dogs to opposite groups
+# then look at disliked dog's disliked dogs and assign them to groups
+# if the disliked dog's disliked dogs groups are already assigned and conflict
+# return false
+# create an array to store group num for each dog
+# create a queue to use to check dog dislikes
+# when happen upon current dog, add to visited
+# for each current dog, assign it's disliked dogs to a group
+
+# time: O(E + N)?
+# space: O(N)
+require 'set'
 
 def possible_bipartition(dislikes)
-  raise NotImplementedError, "possible_bipartition isn't implemented yet"
-end
+
+  return true if dislikes.empty?
+
+  group_nums = [1]
+  q = Queue.new
+  q.enq(0)
+  seen_before = Set.new
+
+  while !q.empty?                     
+    current_dog = q.deq
+    if !seen_before.include?(current_dog)
+      seen_before.add(current_dog)
+      dislikes[current_dog].each do |disliked_dog|
+        if !group_nums[disliked_dog]
+          group_nums[disliked_dog] = group_nums[current_dog] == 1 ? 0 : 1
+          q.enq(disliked_dog)
+        else
+          return false if group_nums[disliked_dog] == group_nums[current_dog]
+        end
+      end
+    end
+    dislikes[current_dog].empty? ? q.enq(1) : current_dog
+  end
+
+  return true
+end