Leah - Water

Gemfile.lock

@@ -0,0 +1,36 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ansi (1.5.0)
+    builder (3.2.4)
+    coderay (1.1.3)
+    method_source (1.0.0)
+    minitest (5.14.2)
+    minitest-reporters (1.4.2)
+      ansi
+      builder
+      minitest (>= 5.0)
+      ruby-progressbar
+    minitest-skip (0.0.3)
+      minitest (~> 5.0)
+    minitest-spec (0.0.2.1)
+      minitest (>= 3.0)
+    pry (0.13.1)
+      coderay (~> 1.1)
+      method_source (~> 1.0)
+    rake (13.0.1)
+    ruby-progressbar (1.10.1)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  minitest
+  minitest-reporters
+  minitest-skip
+  minitest-spec
+  pry
+  rake
+
+BUNDLED WITH
+   2.1.4

lib/linked_list.rb

@@ -7,39 +7,84 @@ def initialize
     @head = nil
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
-  def add_first(data)
+  # Spotify queue
 
+  # Time complexity - O(1)
+  # Space complexity - O(1)
+  def add_first(data)
+    a = Node.new(data)
+    # without next, we lose access to prior nodes. The previous nodes stop existing
+    a.next = @head # next is instance variable on the node object. we set what used to be the head of the linked list to nowbe the node we just created
+    @head = a # this a becomes the new head
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(1)
+  # Space complexity - O(1)
   def get_first
+    return nil if @head.nil?
 
+    return @head.data
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def length
-    return 0
+    length = 0
+    current = @head
+    until current.nil?
+      length += 1
+      current = current.next
+    end
+
+    return length
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def add_last(data)
+    if @head.nil?
+      @head = Node.new(data)
+    else
+      current = @head
+
+      until current.next.nil?
+        current = current.next
+      end
+
+      last = Node.new(data)
+      current.next = last
 
+    end
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def get_last
+    return nil if @head.nil?
+
+    current = @head
 
+    until current.next.nil?
+      current = current.next
+    end
+
+    return current.data
   end
 
-  # Time complexity - ?
-  # Space complexity - ?
+  # Time complexity - O(n)
+  # Space complexity - O(1)
   def get_at_index(index)
+    if @head.nil? || index >= length
+      return nil
+    else
+      current = @head
+      index.times do
+        current = current.next
+      end
+    end
 
+    return current.data
   end
-end
+
+end