Fire - Anna

.gitignore

@@ -0,0 +1 @@
+Gemfile.lock

lib/possible_bipartition.rb

@@ -1,4 +1,47 @@
+# PSEUDOCODE
+# BFS --> queue
+# Groupings array for each dog (size of input array) --> can be 0 or 1 (since bipartition)
+# >> rule will be current_grouping = 1 - current_grouping
+# If a dog / node hasn't been encountered yet (grouping of -1), then add to queue and set grouping
+# If a node grouping ever violates (same as the current node's grouping), then return false
+
+# Time Complexity: O(N+E) -- visit every single node and every one of its edges
+# >> Outer loop: O(n) where n is size of input array
+# >> Inner loop: O(e) where e is the number of edges
+# Space Complexity: O(N)
+# >> Queue depends on size of input array
+# >> groupings array will be size of input array
 
 def possible_bipartition(dislikes)
-  raise NotImplementedError, "possible_bipartition isn't implemented yet"
+  return true if dislikes.empty?
+
+  dog_queue = Queue.new
+  dog_queue << 0
+  dog_groupings = [-1] * dislikes.size
+  current_grouping = 0
+
+  until dog_queue.empty?
+    current_dog = dog_queue.pop
+    if dog_groupings[current_dog] == -1
+      dog_groupings[current_dog] = 1 - current_grouping
+      current_grouping = 1 - current_grouping
+    else
+      current_grouping = dog_groupings[current_dog]
+    end
+
+    disliked_dogs = dislikes[current_dog]
+    disliked_dogs&.each do |dog|
+      return false if dog_groupings[dog] == current_grouping
+
+      if dog_groupings[dog] == -1
+        dog_groupings[dog] = 1 - current_grouping
+        dog_queue << dog
+      end
+    end
+
+    dog_queue << current_dog + 1 if current_dog + 1 < dislikes.size && dog_queue.empty?
+  end
+
+  return true
 end
+

test/possible_bipartition_test.rb

@@ -1,9 +1,10 @@
-require_relative "test_helper"
+require_relative 'test_helper'
 
-describe "possible_bipartition" do
-  it "will work for example 1" do
+describe 'possible_bipartition' do
+  it 'will work for example 1' do
     # Arrange
-    dislikes = [ [],
+    dislikes = [
+      [],
       [2, 3],
       [1, 4],
       [1],
@@ -17,9 +18,10 @@
     expect(answer).must_equal true
   end
 
-  it "will work for example 2" do
+  it 'will work for example 2' do
     # Arrange
-    dislikes =  [ [],
+    dislikes =  [
+      [],
       [2, 3],
       [1, 3],
       [1, 2]
@@ -32,7 +34,7 @@
     expect(answer).must_equal false
   end
 
-  it "will work for example 3" do
+  it 'will work for example 3' do
     # Arrange
     dislikes = [ [],
       [2, 5],
@@ -49,9 +51,10 @@
     expect(answer).must_equal false
   end
 
-  it "will return true for a graph which can be bipartitioned" do
+  it 'will return true for a graph which can be bipartitioned' do
     # Arrange
-    dislikes = [ [3, 6],
+    dislikes = [
+      [3, 6],
       [2, 5],
       [1, 3],
       [0, 2],
@@ -68,9 +71,10 @@
   end
 
 
-  it "will return false for a graph which cannot be bipartitioned" do
+  it 'will return false for a graph which cannot be bipartitioned' do
     # Arrange
-    dislikes = [ [3, 6],
+    dislikes = [
+      [3, 6],
       [2, 5],
       [1, 3],
       [0, 2, 4],
@@ -86,11 +90,11 @@
     expect(answer).must_equal false
   end
 
-  it "will work for an empty graph" do
+  it 'will work for an empty graph' do
     expect(possible_bipartition([])).must_equal true
   end
 
-    it "will return false for a graph which cannot be bipartitioned" do
+    it 'will return false for a graph which cannot be bipartitioned' do
     # Arrange
     dislikes = [ [3, 6],
       [2, 5],