From 04e9ca96277dc3838a7103e72e741957262a464f Mon Sep 17 00:00:00 2001
From: K <774162+kaseea@users.noreply.github.com>
Date: Mon, 26 Aug 2019 08:45:22 -0700
Subject: [PATCH 1/2] some of the stuff

---
 lib/linked_list.rb | 333 +++++++++++++++++++++++++++++----------------
 1 file changed, 216 insertions(+), 117 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 501c60fb..3433bb6e 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -12,152 +12,251 @@ 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
-    end
+  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
-    # Time Complexity:  
-    # Space Complexity
-    def add_first(value)
-      raise NotImplementedError
-    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
+  # Time Complexity:
+  # Space Complexity
+  def add_first(value)
+    new_node = Node.new(value)
+    new_node.next = @head
+    @head = new_node
+  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
+  # 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)
+    node = @head
+    while node != nil
+      if node.data == value
+        return true
+      end
+      node = node.next
     end
+    return false
+  end
 
-    # method to return the max value in the linked list
-    # returns the data value and not the node
-    # Time Complexity:  
-    # Space Complexity
-    def find_max
-      raise NotImplementedError
+  # method to return the max value in the linked list
+  # returns the data value and not the node
+  # Time Complexity:
+  # Space Complexity
+  def find_max
+    if @head == nil
+      return nil
     end
-
-    # 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
+    max = @head.data
+    current = @head
+    while current != nil
+      if current.data > max
+        max = current.data
+      end
+      current = current.next
     end
+    return max
+  end
 
-
-    # method that returns the length of the singly linked list
-    # Time Complexity:  
-    # Space Complexity
-    def length
-      raise NotImplementedError
+  # 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
+    if @head == nil
+      return nil
     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
-    # Time Complexity:  
-    # Space Complexity
-    def get_at_index(index)
-      raise NotImplementedError
+    node = @head
+    min = node.data
+    while node != nil
+      if node.data < min
+        min = node.data
+      end
+      node = node.next
     end
+    return min
+  end
 
-    # method to print all the values in the linked list
-    # Time Complexity:  
-    # Space Complexity
-    def visit
-      raise NotImplementedError
+  # method that returns the length of the singly linked list
+  # Time Complexity:
+  # Space Complexity
+  def length
+    return 0 if !@head
+    length = 0
+    current = @head
+    while current != nil
+      length += 1
+      current = current.next
     end
+    return length
+  end
 
-    # method to delete the first node found with specified value
-    # Time Complexity:  
-    # Space Complexity
-    def delete(value)
-      raise NotImplementedError
+  # 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)
+    length = 0
+    current = @head
+    while current != nil
+      if length == index
+        return current.data
+      end
+      length += 1
+      current = current.next
     end
+    return nil
+  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
+  # method to print all the values in the linked list
+  # Time Complexity:
+  # Space Complexity
+  def visit
+    current = @head
+    while current != nil
+      puts current.data
+      current = current.next
     end
+  end
 
+  # method to delete the first node found with specified value
+  # Time Complexity:
+  # Space Complexity
+  def delete(value)
+    # if self.length != 0
+    #   if @head.data == value
+    #     if @head.next != nil
+    #       @head = @head.next
+    #     else
+    #       @head = nil
+    #     end
+    #   current = @head
+    #   while current.next != nil
+    #     if current.data == value
+    #       current = current.next
+    #     end
+    #     length += 1
+    #     current = current.next
+    #   end
+    # end
+    # return nil
+  end
 
-    ## 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
+  # 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
+    temp = @head
+    puts "temp #{temp} @head #{@head}"
+    puts "length #{self.length}"
+    # while temp.next != nil
+    #   @head = temp.next
+    #   puts "temp #{temp} @head #{@head} temp.next #{temp.next} @head.next #{@head.next}"
+    #   @head.next = temp
+    #   temp = temp.next
+    #   puts "temp #{temp} @head #{@head} temp.next #{temp.next} @head.next #{@head.next}"
+    # end
+    # temp = @head
+    # puts "temp #{temp} @head #{@head}"
+  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
+  ## 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
 
-    # 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
+  # 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
 
+  # 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
 
-    # 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
+  # Additional Exercises
+  # returns the value in the first node
+  # returns nil if the list is empty
+  # Time Complexity:
+  # Space Complexity
+  def get_first
+    if @head == nil
+      return nil
     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
+    if @head.data != nil
+      return @head.data
+    else
+      return nil
     end
+  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
+  # method that inserts a given value as a new last node in the linked list
+  # Time Complexity:
+  # Space Complexity
+  def add_last(value)
+    puts value
+    last = Node.new(value)
+    if @head == nil
+      @head = last
+    else
+      current = @head
+      while current.next != nil
+        current = current.next
+      end
+      current.next = last
     end
+  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
+  # 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
+    return nil if @head == nil
+    val = @head.data
+    current = @head
+    while current != nil
+      val = current.data
+      current = current.next
     end
+    return val
+  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
+  # 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
 
-      # navigate to last node
-      current = @head
-      while current.next != nil
-          current = current.next
-      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
 
-      current.next = @head # make the last node link to first node
+    # 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

From f90b4b8bc132e45b2f597903807a8ce809490d7d Mon Sep 17 00:00:00 2001
From: K <774162+kaseea@users.noreply.github.com>
Date: Tue, 3 Sep 2019 07:03:19 -0700
Subject: [PATCH 2/2] all passing

---
 lib/linked_list.rb | 117 +++++++++++++++++++++++----------------------
 1 file changed, 60 insertions(+), 57 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 3433bb6e..e7ae20d1 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -18,8 +18,8 @@ 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
+  # Time Complexity: O(1)
+  # Space Complexity n?
   def add_first(value)
     new_node = Node.new(value)
     new_node.next = @head
@@ -28,8 +28,8 @@ def add_first(value)
 
   # method to find if the linked list contains a node with specified value
   # returns true if found, false otherwise
-  # Time Complexity:
-  # Space Complexity
+  # Time Complexity: O(n)
+  # Space Complexity O(1)
   def search(value)
     node = @head
     while node != nil
@@ -43,8 +43,8 @@ def search(value)
 
   # method to return the max value in the linked list
   # returns the data value and not the node
-  # Time Complexity:
-  # Space Complexity
+  # Time Complexity: O(n)
+  # Space Complexity O(1)
   def find_max
     if @head == nil
       return nil
@@ -62,8 +62,8 @@ 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
+  # Time Complexity: O(n)
+  # Space Complexity O(1)
   def find_min
     if @head == nil
       return nil
@@ -80,8 +80,8 @@ def find_min
   end
 
   # method that returns the length of the singly linked list
-  # Time Complexity:
-  # Space Complexity
+  # Time Complexity: O(n)
+  # Space Complexity O(1)
   def length
     return 0 if !@head
     length = 0
@@ -96,8 +96,8 @@ 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
+  # Time Complexity: O(n)
+  # Space Complexity O(1)
   def get_at_index(index)
     length = 0
     current = @head
@@ -112,8 +112,8 @@ def get_at_index(index)
   end
 
   # method to print all the values in the linked list
-  # Time Complexity:
-  # Space Complexity
+  # Time Complexity: O(n)
+  # Space Complexity O(1)
   def visit
     current = @head
     while current != nil
@@ -123,45 +123,41 @@ def visit
   end
 
   # method to delete the first node found with specified value
-  # Time Complexity:
-  # Space Complexity
+  # Time Complexity: O(n)
+  # Space Complexity constant
   def delete(value)
-    # if self.length != 0
-    #   if @head.data == value
-    #     if @head.next != nil
-    #       @head = @head.next
-    #     else
-    #       @head = nil
-    #     end
-    #   current = @head
-    #   while current.next != nil
-    #     if current.data == value
-    #       current = current.next
-    #     end
-    #     length += 1
-    #     current = current.next
-    #   end
-    # end
-    # return nil
+    if @head == nil
+      return nil
+    end
+    if @head.data == value
+      @head = @head.next
+    else
+      current = @head
+      while current.next != nil
+        if current.next.data == value
+          current.next = current.next.next
+          break
+        end
+        current = current.next
+      end
+    end
   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
+  # Time Complexity: O(n)
+  # Space Complexity almost constant, needs three pointers allocated
   def reverse
-    temp = @head
-    puts "temp #{temp} @head #{@head}"
-    puts "length #{self.length}"
-    # while temp.next != nil
-    #   @head = temp.next
-    #   puts "temp #{temp} @head #{@head} temp.next #{temp.next} @head.next #{@head.next}"
-    #   @head.next = temp
-    #   temp = temp.next
-    #   puts "temp #{temp} @head #{@head} temp.next #{temp.next} @head.next #{@head.next}"
-    # end
-    # temp = @head
-    # puts "temp #{temp} @head #{@head}"
+    #going to need three pointers
+    prev = nil
+    current = @head
+    while current != nil
+      temp = current.next
+      current.next = prev
+      prev = current
+      current = temp
+    end
+    @head = prev
   end
 
   ## Advanced Exercises
@@ -169,15 +165,21 @@ def reverse
   # Time Complexity:
   # Space Complexity
   def find_middle_value
-    raise NotImplementedError
+    length = self.length
+    return self.get_at_index(length / 2 - 1)
   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
+  # Time Complexity: O(n) + N
+  # Space Complexity O(1)
   def find_nth_from_end(n)
-    raise NotImplementedError
+    length = self.length
+    if n > length
+      return nil
+    else
+      return self.get_at_index(length - n - 1)
+    end
   end
 
   # checks if the linked list has a cycle. A cycle exists if any node in the
@@ -186,14 +188,15 @@ def find_nth_from_end(n)
   # Time Complexity:
   # Space Complexity
   def has_cycle
+    # does this just mean an infinite loop?
     raise NotImplementedError
   end
 
   # Additional Exercises
   # returns the value in the first node
   # returns nil if the list is empty
-  # Time Complexity:
-  # Space Complexity
+  # Time Complexity: O(1)
+  # Space Complexity O(1)
   def get_first
     if @head == nil
       return nil
@@ -206,8 +209,8 @@ def get_first
   end
 
   # method that inserts a given value as a new last node in the linked list
-  # Time Complexity:
-  # Space Complexity
+  # Time Complexity: O(n)
+  # Space Complexity constant + 1?
   def add_last(value)
     puts value
     last = Node.new(value)
@@ -224,8 +227,8 @@ def add_last(value)
 
   # 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
+  # Time Complexity: O(n)
+  # Space Complexity constant
   def get_last
     return nil if @head == nil
     val = @head.data