Branches - Xinran

lib/possible_bipartition.rb

@@ -1,4 +1,40 @@
 
 def possible_bipartition(dislikes)
-  raise NotImplementedError, "possible_bipartition isn't implemented yet"
+  visited = {}
+  q1 = []
+  hash1 = {}
+  q2 = []
+  hash2 = {}
+
+  i = 0
+  while i < dislikes.length
+    if dislikes[i] != [] && !visited[i]
+      q1 << i
+      hash1[i] = true
+      while q1.length > 0 || q2.length > 0
+        return false if !bfs(q1, q2, hash1, hash2, visited, dislikes)
+        return false if !bfs(q2, q1, hash2, hash1, visited, dislikes)
+      end
+    end
+    i += 1
+  end
+  return true
 end
+
+def bfs(q1, q2, hash1, hash2, visited, dislikes)
+  while q1.length > 0
+    dog1 = q1.shift
+    visited[dog1] = true
+    dislikes[dog1].each do |dog|
+      if hash1[dog]
+        return false
+      else
+        if !visited[dog]
+          hash2[dog] = true
+          q2 << dog
+        end
+      end
+    end
+  end
+  return true
+end

test/possible_bipartition_test.rb

@@ -86,6 +86,26 @@
     expect(answer).must_equal false
   end
 
+  it "will return false for a graph which cannot be bipartitioned" do
+    # Arrange
+    dislikes = [ [3, 6],
+      [2, 5],
+      [1, 3],
+      [0, 2, 4],
+      [3, 5],
+      [1, 4],
+      [0],
+      [8],
+      [7]
+    ]
+
+    # Act
+    answer = possible_bipartition(dislikes)
+
+    # Assert
+    expect(answer).must_equal false
+  end
+
   it "will work for an empty graph" do
     expect(possible_bipartition([])).must_equal true
   end