Yolotzin - Time

lib/tree.rb

@@ -1,13 +1,13 @@
 class TreeNode
   attr_reader :key, :value
   attr_accessor :left, :right
-
-   def initialize(key, val)
+  
+  def initialize(key, val)
     @key = key
     @value = val
     @left = nil
     @right = nil
-   end
+  end
 end
 
 class Tree
@@ -16,40 +16,117 @@ def initialize
     @root = nil
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  # Time Complexity: O(log n)
+  # Space Complexity: O(1)
   def add(key, value)
-    raise NotImplementedError
+    new_node = TreeNode.new(key, value)
+    if @root.nil?
+      @root = new_node
+    else
+      add_helper(@root, new_node)
+    end
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def add_helper(current, new_node)
+    return new_node if current.nil?
+    if new_node.key <= current.key
+      current.left = add_helper(current.left, new_node)
+    else
+      current.right = add_helper(current.right, new_node)
+    end
+    return current
+  end
+
+  # Time Complexity: O(log n)
+  # Space Complexity: O(1)
   def find(key)
-    raise NotImplementedError
+    if @root.nil?
+      return nil
+    else
+      find_helper(@root, key)
+    end
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def find_helper(current, key)
+    return nil if current.nil?
+    if key < current.key
+      find_helper(current.left, key)
+    elsif key > current.key
+      find_helper(current.right, key)
+    else
+      return current.value
+    end
+  end
+
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def inorder
-    raise NotImplementedError
+    result = []
+    return inorder_helper(@root, result)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def inorder_helper(current, result)
+    return [] if current.nil?
+    # traverse the left subtree
+    inorder_helper(current.left, result)
+    # visit the current node
+    result << {:key=>current.key, :value => current.value}
+    # traverse the right subtree
+    inorder_helper(current.right, result)
+    return result
+  end
+
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def preorder
-    raise NotImplementedError
+    result = []
+    preorder_helper(@root, result)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def preorder_helper(current, result)
+    return [] if current.nil?
+    # visit the current node
+    result << {:key=>current.key, :value => current.value}
+    # traverse the left subtree
+    preorder_helper(current.left, result)
+    # traverse the right subtree
+    preorder_helper(current.right, result)
+    return result
+  end
+
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def postorder
-    raise NotImplementedError
+    result = []
+    return postorder_helper(@root, result)
   end
 
-  # Time Complexity: 
-  # Space Complexity: 
+  def postorder_helper(current, result)
+    return [] if current.nil?
+    # traverse the left subtree
+    postorder_helper(current.left, result)
+    # traverse the right subtree
+    postorder_helper(current.right, result)
+    # visit the current node
+    result << {:key=>current.key, :value => current.value}
+  end
+
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
   def height
-    raise NotImplementedError
+    return 0 if @root.nil?
+    return height_helper(@root)
+  end
+
+  def height_helper(current)
+    return 0 if current.nil?
+    # Otherwise return 1 plus the maximum of the heights of the right and left subtrees
+    heights = []
+    right_height = height_helper(current.right)
+    left_height = height_helper(current.left)
+    heights << right_height
+    heights << left_height
+    return heights.max + 1
   end
 
   # Optional Method
@@ -63,4 +140,4 @@ def bfs
   def to_s
     return "#{self.inorder}"
   end
-end
+end