From 30fae6310a413784b4812600c34c99131a7b9db8 Mon Sep 17 00:00:00 2001
From: Morgan Schuler <morganlschuler@gmail.com>
Date: Wed, 19 Feb 2020 19:52:16 -0800
Subject: [PATCH 1/3] Linked list exercises

---
 lib/linked_list.rb | 340 ++++++++++++++++++++++++++++++++-------------
 1 file changed, 241 insertions(+), 99 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 8dee5e8d..6e51904e 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -3,7 +3,7 @@
 class Node
   attr_reader :data # allow external entities to read value but not write
   attr_accessor :next # allow external entities to read or write next node
-
+  
   def initialize(value, next_node = nil)
     @data = value
     @next = next_node
@@ -12,120 +12,262 @@ def initialize(value, next_node = nil)
 
 # Defines the singly linked list
 class LinkedList
-    def initialize
-      @head = nil # keep the head private. Not accessible outside this class
+  def initialize
+    @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)
+    @head = Node.new(value)
+  end
+  
+  # method to find if the linked list contains a node with specified value
+  # returns true if found, false otherwise
+  def search(value)
+    current = @head
+    
+    until current.nil?
+      return true if current.data == value
+      current = current.next
     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
+    return false
+  end
+  
+  # method to return the max value in the linked list
+  # returns the data value and not the node
+  def find_max
+    if @head == nil
+      return nil
     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
+    max = @head.data
+    
+    until current == nil
+      if current.data > max
+        max = current.data
+      end
+      current = current.next
     end
-
-    # method to return the max value in the linked list
-    # returns the data value and not the node
-    def find_max
-      raise NotImplementedError
+    return max
+  end
+  
+  # method to return the min value in the linked list
+  # returns the data value and not the node
+  def find_min
+    if @head == nil
+      return nil
     end
-
-    # method to return the min value in the linked list
-    # returns the data value and not the node
-    def find_min
-      raise NotImplementedError
+    
+    current = @head
+    min = @head.data
+    
+    until current == nil
+      if current.data < min
+        min = current.data
+      end
+      current = current.next
     end
-
-
-    # method that returns the length of the singly linked list
-    def length
-      raise NotImplementedError
+    return min
+  end
+  
+  
+  # method that returns the length of the singly linked list
+  def length
+    if @head.nil?
+      return 0
     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
+    
+    current = @head
+    count = 0
+    
+    until current.nil?
+      count += 1
+      current = current.next
     end
-
-    # method to print all the values in the linked list
-    def visit
-      raise NotImplementedError
+    return count
+  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)
+    count = 0
+    current = @head
+    until count == index
+      return nil if current.nil?
+      current = current.next
+      count += 1
     end
-
-    # method to delete the first node found with specified value
-    def delete(value)
-      raise NotImplementedError
+    return current.data
+  end
+  
+  # method to print all the values in the linked list
+  def visit
+    current = @head
+    
+    until current.nil?
+      print current.data
     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
+  end
+  
+  # method to delete the first node found with specified value
+  def delete(value)
+    current = @head
+    previous = nil
+    
+    return nil if current.nil?
+    
+    until current.data == value
+      return nil if current.nil?
+      previous = current
+      current = current.next
     end
-
-
-    ## Advanced Exercises
-    # returns the value at the middle element in the singly linked list
-    def find_middle_value
-      raise NotImplementedError
+    
+    if previous.nil?
+      @head = current.next
+    else
+      previous.next = current.next
     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
+  end
+  
+  # method to reverse the singly linked list
+  # note: the nodes should be moved and not just the values in the nodes
+  def reverse
+    return if @head.nil?
+    current = @head
+    previous = nil
+    
+    until current.next.nil?
+      temp = current.next
+      current.next = previous
+      previous = current
+      current = temp
     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
+    
+    current.next = previous
+    @head = current
+  end
+  
+  
+  ## Advanced Exercises
+  # returns the value at the middle element in the singly linked list
+  def find_middle_value
+    length = self.length
+    
+    return nil if @head.nil?
+    
+    if length % 2 == 0
+      value = (length / 2) - 1
+    else
+      value = (length / 2)
     end
-
-
-    # Additional Exercises 
-    # returns the value in the first node
-    # returns nil if the list is empty
-    def get_first
-      raise NotImplementedError
+    return self.get_at_index(value)
+  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)
+    current = @head
+    n_ahead = @head
+    
+    return nil if current.nil?
+    
+    n.times do
+      return nil if n_ahead.next.nil?
+      n_ahead = n_ahead.next
     end
-
-    # method that inserts a given value as a new last node in the linked list
-    def add_last(value)
-      raise NotImplementedError
+    
+    until n_ahead.next.nil?
+      return current.data if current.next.nil?
+      current = current.next
+      n_ahead = n_ahead.next
     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 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
+  end
+  
+  
+  # Additional Exercises 
+  # returns the value in the first node
+  # returns nil if the list is empty
+  def get_first
+    if @head.nil?
+      return nil
+    else
+      return @head.data
     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
+  end
+  
+  # method that inserts a given value as a new last node in the linked list
+  def add_last(value)
+    current = @head
+    
+    if current.nil?
+      @head = Node.new(value)
+      return @head
     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
+    
+    until current.next == nil
+      current = current.next
+    end
+    current.next = Node.new(value)
+  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
+    current = @head
+    
+    return nil if current.nil?
+    
+    until current.next.nil?
+      current = current.next
+    end
+    
+    return current.data
+  end
+  
+  # method to insert a new node with specific data value, assuming the linked
+  # list is sorted in ascending order
+  def insert_ascending(value)
+    current = @head
+    
+    if current.nil?
+      return @head = Node.new(value)
+    end
+    
+    until current.nil?
+      if value >= current.data && value < current.next.data
+        new_node = Node.new(value, current.next)
+        current.next = new_node
+        return
+      else
+        current = current.next
       end
-
-      current.next = @head # make the last node link to first node
     end
-end
+    current = Node.new(value)
+  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
+  end
+end
\ No newline at end of file

From 4aa856883ec89a7d2f14774b3d664ea0c0d394eb Mon Sep 17 00:00:00 2001
From: Morgan Schuler <morganlschuler@gmail.com>
Date: Wed, 19 Feb 2020 20:18:14 -0800
Subject: [PATCH 2/3] Updates

---
 lib/linked_list.rb | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 6e51904e..e76d21b1 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -93,13 +93,13 @@ def length
   # 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)
-    count = 0
     current = @head
-    until count == index
+    
+    index.times do
       return nil if current.nil?
       current = current.next
-      count += 1
     end
+    
     return current.data
   end
   
@@ -117,7 +117,9 @@ def delete(value)
     current = @head
     previous = nil
     
-    return nil if current.nil?
+    if current == nil
+      return nil
+    end
     
     until current.data == value
       return nil if current.nil?
@@ -125,7 +127,7 @@ def delete(value)
       current = current.next
     end
     
-    if previous.nil?
+    if previous == nil
       @head = current.next
     else
       previous.next = current.next
@@ -170,19 +172,19 @@ def find_middle_value
   # assume indexing starts at 0 while counting to n
   def find_nth_from_end(n)
     current = @head
-    n_ahead = @head
+    n_from_end = @head
     
     return nil if current.nil?
     
     n.times do
-      return nil if n_ahead.next.nil?
-      n_ahead = n_ahead.next
+      return nil if n_from_end.next.nil?
+      n_from_end = n_from_end.next
     end
     
-    until n_ahead.next.nil?
+    until n_from_end.next.nil?
       return current.data if current.next.nil?
       current = current.next
-      n_ahead = n_ahead.next
+      n_from_end = n_from_end.next
     end
     return current.data
   end

From b77e5e02c389c388ee8d4b9ef39e48561f48b641 Mon Sep 17 00:00:00 2001
From: Morgan Schuler <morganlschuler@gmail.com>
Date: Thu, 20 Feb 2020 08:04:22 -0800
Subject: [PATCH 3/3] Fixes

---
 lib/linked_list.rb | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index e76d21b1..5733636b 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -140,6 +140,7 @@ def reverse
     return if @head.nil?
     current = @head
     previous = nil
+    temp = nil
     
     until current.next.nil?
       temp = current.next
@@ -168,7 +169,7 @@ def find_middle_value
     return self.get_at_index(value)
   end
   
-  # find the nth node from the end and return its value
+  # find the nth node from the end and return it s value
   # assume indexing starts at 0 while counting to n
   def find_nth_from_end(n)
     current = @head