From cce9b058055ff993e959b87dbd1d9de1746cd104 Mon Sep 17 00:00:00 2001
From: shrutivanw <shruti@adadevelopersacademy.org>
Date: Tue, 26 Feb 2019 00:34:18 -0800
Subject: [PATCH 01/13] Updating solution

Adding solution
---
 linked_list.rb | 266 ++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 221 insertions(+), 45 deletions(-)

diff --git a/linked_list.rb b/linked_list.rb
index c07cdaa7..29e90430 100644
--- a/linked_list.rb
+++ b/linked_list.rb
@@ -13,116 +13,292 @@ def initialize(value)
 # Defines the singly linked list
 class LinkedList
     def initialize
-        @head = nil # keep the head private. Not accessible outside this class
+      @head = nil # keep the head private. Not accessible outside this class
     end
-
+  
     # method to add a new node with the specific data value in the linked list
     # insert the new node at the beginning of the linked list
     def add_first(value)
-        raise NotImplementedError
+        new_node = Node.new(value)
+  
+        if @head != nil # if linked list is not empty
+          new_node.next = @head
+        end
+  
+        @head = new_node
     end
-
+  
     # returns the value in the first node
     # returns nil if the list is empty
     def get_first
-        raise NotImplementedError
+      return nil if !@head
+      return @head.data
     end
-
+  
     # method to find if the linked list contains a node with specified value
     # returns true if found, false otherwise
     def search(value)
-        raise NotImplementedError
+        current = @head
+        while current != nil
+          if current.data == value
+            return true
+          end
+          current = current.next
+        end
+  
+        return false
     end
-
+  
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max
-        raise NotImplementedError
+        if @head == nil # empty list case
+          # puts "Error: The linked list is empty. Cannot compute max."
+          return nil
+        end
+  
+        current = @head
+        max = current.data
+        current = current.next
+        while current != nil
+          if current.data > max
+            max = current.data
+          end
+          current = current.next
+        end
+        return max
     end
-
+  
     # method to return the min value in the linked list
     # returns the data value and not the node
     def find_min
-        raise NotImplementedError
+        if @head == nil # empty list case
+          # puts "Error: The linked list is empty. Cannot compute min."
+          return nil
+        end
+  
+        current = @head
+        min = current.data
+        current = current.next
+        while current != nil
+          if current.data < min
+            min = current.data
+          end
+          current = current.next
+        end
+        return min
     end
-
+  
     # method that returns the length of the singly linked list
     def length
-        raise NotImplementedError
+        count = 0
+        current = @head
+        while current != nil
+          count += 1
+          current = current.next
+        end
+  
+        return count
     end
-
+  
     # method that inserts a given value as a new last node in the linked list
     def add_last(value)
-        raise NotImplementedError
+      new_node = Node.new(value)
+  
+      if !@head
+          @head = new_node
+          return
+      end
+  
+      current = @head
+      while current.next
+          current = current.next
+      end
+      current.next = new_node
+      return
     end
-
+  
     # method that returns the value of the last node in the linked list
     # returns nil if the linked list is empty
     def get_last
-        raise NotImplementedError
+      return nil if !@head
+      current = @head
+      while current.next
+          current = current.next
+      end
+      return current.data
     end
-
+  
     # method that returns the value at a given index in the linked list
     # index count starts at 0
     # returns nil if there are fewer nodes in the linked list than the index value
     def get_at_index(index)
-        raise NotImplementedError
+        i = 0
+        current = @head
+        while current != nil
+          if i == index
+            return current.data
+          end
+          current = current.next
+          i += 1
+        end
+        # puts "Error: #{index} exceeds the linked list length."
+        return nil
     end
-
-
+  
+  
     # method to insert a new node with specific data value, assuming the linked
     # list is sorted in ascending order
     def insert_ascending(value)
-        raise NotImplementedError
+        new_node = Node.new(value)
+  
+        # check for new_node being the new head case
+        if @head == nil || value <= @head.data
+          new_node.next = @head
+          @head = new_node
+          return
+        end
+  
+        current = @head
+        while current.next != nil && current.next.data < value
+          current = current.next
+        end
+        new_node.next = current.next
+        current.next = new_node
     end
-
+  
     # method to print all the values in the linked list
     def visit
-        raise NotImplementedError
+        current = @head
+        while current != nil
+          print "#{current.data} "
+          current = current.next
+        end
+        puts
     end
-
+  
     # method to delete the first node found with specified value
     def delete(value)
-        raise NotImplementedError
+        if @head == nil
+          return
+        end
+  
+        # account for case: node to delete is current head
+        if @head.data == value
+          @head = @head.next
+          return
+        end
+  
+        current = @head
+        while current.next != nil
+          if current.next.data == value
+            current.next = current.next.next
+            return
+          end
+          current = current.next
+        end
+        # value to be deleted was not found if the control flow reaches here
     end
-
+  
     # method to reverse the singly linked list
     # note: the nodes should be moved and not just the values in the nodes
     def reverse
-        raise NotImplementedError
+        current = @head
+        previous = nil
+        while current != nil
+          temp = current.next # save state
+          current.next = previous # update link
+  
+          # move to next
+          previous = current
+          current = temp
+        end
+        @head = previous
     end
-
+  
     ## Advanced Exercises
     # returns the value at the middle element in the singly linked list
     def find_middle_value
-        raise NotImplementedError
+        if @head == nil
+          return nil
+        end
+  
+        slow = @head
+        fast = @head.next
+        while fast != nil
+          slow = slow.next
+          fast = fast.next
+          if fast != nil
+            fast = fast.next
+          end
+        end
+        return slow.data
     end
-
+  
     # find the nth node from the end and return its value
     # assume indexing starts at 0 while counting to n
     def find_nth_from_end(n)
-        raise NotImplementedError
+        # approach with going through the linked list just once
+        current = @head
+        index = 0
+        # count to n from the beginning
+        while current != nil && index != n
+          current = current.next
+          index += 1
+        end
+  
+        # check that we didn't reach the end
+        if current == nil
+          # puts "Error: The linked list has less than #{n} indexable nodes"
+          return nil
+        end
+  
+        # the previous while loop exited because of index == n condition
+        # start a new traverser at the beginning.
+        # when current reaches the end, new_current will be at index n from the end
+        new_current = @head
+        while current.next != nil
+          current = current.next
+          new_current = new_current.next
+        end
+        return new_current.data
     end
-
+  
     # checks if the linked list has a cycle. A cycle exists if any node in the
     # linked list links to a node already visited.
     # returns true if a cycle is found, false otherwise.
     def has_cycle
-        raise NotImplementedError
+        if @head == nil || @head.next == nil
+          return false
+        end
+        slow = @head
+        fast = @head
+        while fast != nil
+          slow = slow.next
+          fast = fast.next
+          if fast != nil
+            fast = fast.next
+          end
+          if slow == fast
+            return true # cycle detected
+          end
+        end
+        return false # reached the end of the linked list - no cycle detected
     end
-
+  
     # Helper method for tests
     # Creates a cycle in the linked list for testing purposes
     # Assumes the linked list has at least one node
     def create_cycle
-        return if @head == nil # don't do anything if the linked list is empty
-
-        # navigate to last node
-        current = @head
-        while current.next != nil
-            current = current.next
-        end
-
-        current.next = @head # make the last node link to first node
+      return if @head == nil # don't do anything if the linked list is empty
+  
+      # navigate to last node
+      current = @head
+      while current.next != nil
+        current = current.next
+      end
+  
+      current.next = @head # make the last node link to first node
     end
-end
+  end
+  

From 720e2bf50dbc40c6302ae15f2ee009fe9e48d13b Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 13 Aug 2020 14:10:20 -0700
Subject: [PATCH 02/13] dockerize stuff

---
 Dockerfile | 25 +++++++++++++++++++++++++
 Gemfile    |  8 ++++++++
 test.sh    |  0
 3 files changed, 33 insertions(+)
 create mode 100644 Dockerfile
 create mode 100644 Gemfile
 create mode 100644 test.sh

diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 00000000..f1ffa4fb
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,25 @@
+# Starting from a minimalist image
+FROM ruby:2.7
+# Reference for help contact me
+LABEL maintainer="chris@adadev.org"
+
+# Create a directory for the app
+RUN mkdir /app
+
+# Set the working directory for RUN, ADD and COPY
+WORKDIR /app
+
+# Add entire student fork (overwrites previously added files)
+ARG SUBMISSION_SUBFOLDER
+ADD $SUBMISSION_SUBFOLDER /app
+
+
+COPY ./Gemfile .
+RUN gem install bundler
+RUN bundle install
+
+# Overwrite the script and test files
+ADD test.sh /app
+ADD test /app
+
+RUN chmod +x test.sh
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 00000000..0aab9c2c
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+source "https://rubygems.org"
+
+gem 'rake'
+gem 'minitest'
+gem 'minitest-spec'
+gem 'minitest-reporters'
+gem "pry"
\ No newline at end of file
diff --git a/test.sh b/test.sh
new file mode 100644
index 00000000..e69de29b

From a3519cb7be459435ecdbb1cfaf7041a521dc94eb Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 13 Aug 2020 14:11:14 -0700
Subject: [PATCH 03/13] update test.sh

---
 test.sh | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/test.sh b/test.sh
index e69de29b..8509a009 100644
--- a/test.sh
+++ b/test.sh
@@ -0,0 +1,3 @@
+#!/bin/bash
+
+rake

From f83442dfd48aab2ed2b0e8900b548d531662b21b Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 13 Aug 2020 14:11:52 -0700
Subject: [PATCH 04/13] dockerize stuff

---
 Dockerfile   | 25 +++++++++++++++++++++++++
 Gemfile      |  8 ++++++++
 Gemfile.lock | 33 +++++++++++++++++++++++++++++++++
 test.sh      |  3 +++
 4 files changed, 69 insertions(+)
 create mode 100644 Dockerfile
 create mode 100644 Gemfile
 create mode 100644 Gemfile.lock
 create mode 100644 test.sh

diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 00000000..f1ffa4fb
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,25 @@
+# Starting from a minimalist image
+FROM ruby:2.7
+# Reference for help contact me
+LABEL maintainer="chris@adadev.org"
+
+# Create a directory for the app
+RUN mkdir /app
+
+# Set the working directory for RUN, ADD and COPY
+WORKDIR /app
+
+# Add entire student fork (overwrites previously added files)
+ARG SUBMISSION_SUBFOLDER
+ADD $SUBMISSION_SUBFOLDER /app
+
+
+COPY ./Gemfile .
+RUN gem install bundler
+RUN bundle install
+
+# Overwrite the script and test files
+ADD test.sh /app
+ADD test /app
+
+RUN chmod +x test.sh
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 00000000..0aab9c2c
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+source "https://rubygems.org"
+
+gem 'rake'
+gem 'minitest'
+gem 'minitest-spec'
+gem 'minitest-reporters'
+gem "pry"
\ No newline at end of file
diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 00000000..116502cc
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,33 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    ansi (1.5.0)
+    builder (3.2.4)
+    coderay (1.1.3)
+    method_source (1.0.0)
+    minitest (5.14.1)
+    minitest-reporters (1.4.2)
+      ansi
+      builder
+      minitest (>= 5.0)
+      ruby-progressbar
+    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-spec
+  pry
+  rake
+
+BUNDLED WITH
+   2.1.4
diff --git a/test.sh b/test.sh
new file mode 100644
index 00000000..8509a009
--- /dev/null
+++ b/test.sh
@@ -0,0 +1,3 @@
+#!/bin/bash
+
+rake

From 4a702b9633be176c2b075b1cb37ce53785fce7c8 Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 13 Aug 2020 14:12:15 -0700
Subject: [PATCH 05/13] rakefile

---
 Rakefile | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 Rakefile

diff --git a/Rakefile b/Rakefile
new file mode 100644
index 00000000..ce1d5e9e
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,11 @@
+
+require 'rake/testtask'
+
+Rake::TestTask.new do |t|
+  t.libs = ["lib"]
+  t.warning = true
+  t.test_files = FileList['test/*_test.rb']
+end
+
+task default: :test
+

From a22edcdc3d4099ab1094f15d12423ea17f433ef6 Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 13 Aug 2020 14:13:07 -0700
Subject: [PATCH 06/13] organize files

---
 linked_list.rb => lib/linked_list.rb            | 0
 linked_list_spec.rb => test/linked_list_test.rb | 0
 2 files changed, 0 insertions(+), 0 deletions(-)
 rename linked_list.rb => lib/linked_list.rb (100%)
 rename linked_list_spec.rb => test/linked_list_test.rb (100%)

diff --git a/linked_list.rb b/lib/linked_list.rb
similarity index 100%
rename from linked_list.rb
rename to lib/linked_list.rb
diff --git a/linked_list_spec.rb b/test/linked_list_test.rb
similarity index 100%
rename from linked_list_spec.rb
rename to test/linked_list_test.rb

From 6d13814d1c93eda4ee144412cf507fd6cbc93c17 Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 13 Aug 2020 14:14:04 -0700
Subject: [PATCH 07/13] fix path to linked_list file

---
 test/linked_list_test.rb | 2 +-
 test/test_helper.rb      | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 test/test_helper.rb

diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb
index d7302e9f..d6e1a0c1 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -2,7 +2,7 @@
 require 'minitest/reporters'
 require 'minitest/skip_dsl'
 
-require_relative 'linked_list'
+require_relative '../lib/linked_list'
 
 
 Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
diff --git a/test/test_helper.rb b/test/test_helper.rb
new file mode 100644
index 00000000..039f0234
--- /dev/null
+++ b/test/test_helper.rb
@@ -0,0 +1,8 @@
+require 'minitest'
+require 'minitest/autorun'
+require 'minitest/reporters'
+
+Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new
+
+require_relative '../lib/linked_list'
+

From 62988281a6d91576baa3943b95d9bd3bed3949a0 Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 13 Aug 2020 14:34:16 -0700
Subject: [PATCH 08/13] add minitest-skip

---
 Gemfile      | 4 +++-
 Gemfile.lock | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/Gemfile b/Gemfile
index 0aab9c2c..04a9dcdd 100644
--- a/Gemfile
+++ b/Gemfile
@@ -5,4 +5,6 @@ gem 'rake'
 gem 'minitest'
 gem 'minitest-spec'
 gem 'minitest-reporters'
-gem "pry"
\ No newline at end of file
+gem "pry"
+gem 'minitest-skip'
+
diff --git a/Gemfile.lock b/Gemfile.lock
index 116502cc..878af75d 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -11,6 +11,8 @@ GEM
       builder
       minitest (>= 5.0)
       ruby-progressbar
+    minitest-skip (0.0.1)
+      minitest (~> 5.0)
     minitest-spec (0.0.2.1)
       minitest (>= 3.0)
     pry (0.13.1)
@@ -25,6 +27,7 @@ PLATFORMS
 DEPENDENCIES
   minitest
   minitest-reporters
+  minitest-skip
   minitest-spec
   pry
   rake

From 3cbac36b958eaac989d355694b0e971b76d829db Mon Sep 17 00:00:00 2001
From: Chris M <chris@adadevelopersacademy.org>
Date: Thu, 20 Aug 2020 11:57:15 -0700
Subject: [PATCH 09/13] Update linked_list.rb

---
 lib/linked_list.rb | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 8dee5e8d..0de1ee00 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -18,12 +18,16 @@ def initialize
 
     # method to add a new node with the specific data value in the linked list
     # insert the new node at the beginning of the linked list
+    # Time Complexity: ?
+    # Space Complexity: ?
     def add_first(value)
       raise NotImplementedError
     end
 
     # method to find if the linked list contains a node with specified value
     # returns true if found, false otherwise
+    # Time Complexity: ?
+    # Space Complexity: ?
     def search(value)
       raise NotImplementedError
     end
@@ -36,12 +40,16 @@ def find_max
 
     # method to return the min value in the linked list
     # returns the data value and not the node
+    # Time Complexity: ?
+    # Space Complexity: ?
     def find_min
       raise NotImplementedError
     end
 
 
     # method that returns the length of the singly linked list
+    # Time Complexity: ?
+    # Space Complexity: ?
     def length
       raise NotImplementedError
     end
@@ -49,22 +57,30 @@ def length
     # method that returns the value at a given index in the linked list
     # index count starts at 0
     # returns nil if there are fewer nodes in the linked list than the index value
+    # Time Complexity: ?
+    # Space Complexity: ?
     def get_at_index(index)
       raise NotImplementedError
     end
 
     # method to print all the values in the linked list
+    # Time Complexity: ?
+    # Space Complexity: ?
     def visit
       raise NotImplementedError
     end
 
     # method to delete the first node found with specified value
+    # Time Complexity: ?
+    # Space Complexity: ?
     def delete(value)
       raise NotImplementedError
     end
 
     # method to reverse the singly linked list
     # note: the nodes should be moved and not just the values in the nodes
+    # Time Complexity: ?
+    # Space Complexity: ?
     def reverse
       raise NotImplementedError
     end
@@ -72,12 +88,16 @@ def reverse
 
     ## Advanced Exercises
     # returns the value at the middle element in the singly linked list
+    # Time Complexity: ?
+    # Space Complexity: ?
     def find_middle_value
       raise NotImplementedError
     end
 
     # find the nth node from the end and return its value
     # assume indexing starts at 0 while counting to n
+    # Time Complexity: ?
+    # Space Complexity: ?
     def find_nth_from_end(n)
       raise NotImplementedError
     end
@@ -85,6 +105,8 @@ def find_nth_from_end(n)
     # checks if the linked list has a cycle. A cycle exists if any node in the
     # linked list links to a node already visited.
     # returns true if a cycle is found, false otherwise.
+    # Time Complexity: ?
+    # Space Complexity: ?
     def has_cycle
       raise NotImplementedError
     end
@@ -93,23 +115,31 @@ def has_cycle
     # Additional Exercises 
     # returns the value in the first node
     # returns nil if the list is empty
+    # Time Complexity: ?
+    # Space Complexity: ?
     def get_first
       raise NotImplementedError
     end
 
     # method that inserts a given value as a new last node in the linked list
+    # Time Complexity: ?
+    # Space Complexity: ?
     def add_last(value)
       raise NotImplementedError
     end
 
     # method that returns the value of the last node in the linked list
     # returns nil if the linked list is empty
+    # Time Complexity: ?
+    # Space Complexity: ?
     def get_last
       raise NotImplementedError
     end
 
     # method to insert a new node with specific data value, assuming the linked
     # list is sorted in ascending order
+    # Time Complexity: ?
+    # Space Complexity: ?
     def insert_ascending(value)
       raise NotImplementedError
     end

From e444f3fde34134ea54d4903f778206e6d276b4b7 Mon Sep 17 00:00:00 2001
From: CheezItMan <chris@adadevelopersacademy.org>
Date: Thu, 20 Aug 2020 18:51:25 -0700
Subject: [PATCH 10/13] modify tests for optionals

---
 test/linked_list_test.rb | 80 ++++++++++++++++++++--------------------
 1 file changed, 40 insertions(+), 40 deletions(-)

diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb
index d169c9a0..c1756935 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -27,7 +27,7 @@
             @list.add_first(3)
 
             # Assert
-            expect(@list.get_first).must_equal 3
+            expect(@list.get_at_index(0)).must_equal 3
         end
 
         it 'will put the last added item to the front of the list' do
@@ -36,18 +36,18 @@
             @list.add_first(2)
 
             # Assert
-            expect(@list.get_first).must_equal 2
+            expect(@list.get_at_index(0)).must_equal 2
 
             # Act again
             @list.add_first(3)
 
             # Assert
-            expect(@list.get_first).must_equal 3
+            expect(@list.get_at_index(0)).must_equal 3
         end
 
         it 'will return `nil` for `getFirst` if the list is empty' do
 
-            expect(@list.get_first).must_be_nil
+            expect(@list.get_at_index(0)).must_be_nil
         end
     end
 
@@ -89,10 +89,28 @@
         end
     end
 
-    describe "addLast & getLast" do
+    describe 'get_at_index' do
+        it 'returns nil if the index is outside the bounds of the list' do
+            expect(@list.get_at_index(3)).must_be_nil
+        end
+
+        it 'can retrieve an item at an index in the list' do
+            @list.add_first(1)
+            @list.add_first(2)
+            @list.add_first(3)
+            @list.add_first(4)
+
+            expect(@list.get_at_index(0)).must_equal 4
+            expect(@list.get_at_index(1)).must_equal 3
+            expect(@list.get_at_index(2)).must_equal 2
+            expect(@list.get_at_index(3)).must_equal 1
+        end
+    end
+
+    xdescribe "Optional addLast & getLast" do
         it "will add to the front if the list is empty" do
             @list.add_last(1)
-            expect(@list.get_first).must_equal 1
+            expect(@list.get_at_index(0)).must_equal 1
         end
 
         it "will put new items to the rear of the list" do
@@ -101,35 +119,17 @@
             expect(@list.get_last).must_equal 2
 
             @list.add_last(3)
-            expect(@list.get_first).must_equal 2
+            expect(@list.get_at_index(0)).must_equal 2
             expect(@list.get_last).must_equal 3
             expect(@list.length).must_equal 2
 
             @list.add_last(4)
-            expect(@list.get_first).must_equal 2
+            expect(@list.get_at_index(0)).must_equal 2
             expect(@list.get_last).must_equal 4
             expect(@list.length).must_equal 3
         end
     end
 
-    describe 'get_at_index' do
-        it 'returns nil if the index is outside the bounds of the list' do
-            expect(@list.get_at_index(3)).must_be_nil
-        end
-
-        it 'can retrieve an item at an index in the list' do
-            @list.add_first(1)
-            @list.add_first(2)
-            @list.add_first(3)
-            @list.add_first(4)
-
-            expect(@list.get_at_index(0)).must_equal 4
-            expect(@list.get_at_index(1)).must_equal 3
-            expect(@list.get_at_index(2)).must_equal 2
-            expect(@list.get_at_index(3)).must_equal 1
-        end
-    end
-
     describe 'max and min values' do
         it 'returns nil if the list is empty' do
             expect(@list.find_max()).must_be_nil
@@ -145,7 +145,7 @@
                 count += 1
             end
 
-            @list.add_last(100)
+            @list.add_first(100)
             @list.add_first(-12)
             expect(@list.find_max).must_equal 100
             expect(@list.find_min).must_equal(-12)
@@ -160,8 +160,8 @@
         end
 
         it "can delete valid values from list" do
-            @list.add_last(9)
-            @list.add_last(10)
+            @list.add_first(9)
+            @list.add_first(10)
             @list.add_first(4)
             @list.add_first(3)
             @list.add_first(2)
@@ -170,29 +170,29 @@
             @list.delete(2)
             expect(@list.get_first).must_equal 3
             expect(@list.length).must_equal 4
-            expect(@list.get_last).must_equal 10
+            expect(@list.get_at_index(@list.length - 1)).must_equal 9
             expect(@list.find_max).must_equal 10
             expect(@list.find_min).must_equal 3
 
             # delete last node
             @list.delete(10)
-            expect(@list.get_first).must_equal 3
+            expect(@list.get_at_index(0)).must_equal 3
             expect(@list.length).must_equal 3
-            expect(@list.get_last).must_equal 9
+            expect(@list.get_at_index(@list.length - 1)).must_equal 9
             expect(@list.find_max).must_equal 9
             expect(@list.find_min).must_equal 3
 
-            # delete fist node (requires updating head)
+            # delete first node (requires updating head)
             @list.delete(4)
-            expect(@list.get_first).must_equal 3
+            expect(@list.get_at_index(0)).must_equal 3
             expect(@list.length).must_equal 2
-            expect(@list.get_last).must_equal 9
+            expect(@list.get_at_index(@list.length - 1)).must_equal 9
             expect(@list.find_max).must_equal 9
             expect(@list.find_min).must_equal 3
         end
     end
 
-    describe "nth_from_the_end" do
+    xdescribe "Optional:  nth_from_the_end" do
         it 'returns nil if n is outside the bounds of the list' do
             expect(@list.find_nth_from_end(3)).must_be_nil
         end
@@ -219,10 +219,10 @@
             @list.add_first(1)
             @list.reverse
 
-            expect(@list.find_nth_from_end(0)).must_equal 1
-            expect(@list.find_nth_from_end(1)).must_equal 2
-            expect(@list.find_nth_from_end(2)).must_equal 3
-            expect(@list.find_nth_from_end(3)).must_equal 4
+            expect(@list.get_at_index(0)).must_equal 4
+            expect(@list.get_at_index(1)).must_equal 3
+            expect(@list.get_at_index(2)).must_equal 2
+            expect(@list.get_at_index(3)).must_equal 1
         end
     end
 end

From 137cbdd62ec733ac1435078055d00c53ea3e898c Mon Sep 17 00:00:00 2001
From: Chris M <chris@adadevelopersacademy.org>
Date: Sat, 22 Aug 2020 09:47:46 -0700
Subject: [PATCH 11/13] Update README.md

---
 README.md | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/README.md b/README.md
index e38d64fc..a1f2d313 100644
--- a/README.md
+++ b/README.md
@@ -8,11 +8,4 @@ Design and implement the classes and the methods. Implement the methods within t
 
 ### Going Further
 
-Create a new class called `DoublyLinkedList` which implements a doubly linked list.  Then implement the following methods:  
-
-- `add_first`
-- `add_last`
-- `get_first`
-- `get_at_index(index)`
-- `reverse`
-- `delete(value)`
+There are a set of advanced methods you can choose to implement for additional practice.

From 76d8327a268210278fcaffdc0d997f947cc9be33 Mon Sep 17 00:00:00 2001
From: Chris M <chris@adadevelopersacademy.org>
Date: Mon, 24 Aug 2020 21:46:42 -0700
Subject: [PATCH 12/13] Update linked_list_test.rb

---
 test/linked_list_test.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb
index c1756935..75df0d6e 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -168,7 +168,7 @@
 
             # delete fist node (requires updating head)
             @list.delete(2)
-            expect(@list.get_first).must_equal 3
+            expect(@list.get_at_index(0)).must_equal 3
             expect(@list.length).must_equal 4
             expect(@list.get_at_index(@list.length - 1)).must_equal 9
             expect(@list.find_max).must_equal 10

From 75dd4376dd28130dd6de5b64ed7e715f09da642c Mon Sep 17 00:00:00 2001
From: Chris M <chris@adadevelopersacademy.org>
Date: Sun, 14 Mar 2021 10:40:07 -0700
Subject: [PATCH 13/13] Update linked_list_test.rb

---
 test/linked_list_test.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb
index 75df0d6e..7c695018 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -166,7 +166,7 @@
             @list.add_first(3)
             @list.add_first(2)
 
-            # delete fist node (requires updating head)
+            # delete first node (requires updating head)
             @list.delete(2)
             expect(@list.get_at_index(0)).must_equal 3
             expect(@list.length).must_equal 4