From a63530b61f1702d37bf8b5e2b6ecabf9c3fe745d Mon Sep 17 00:00:00 2001
From: Alice <alicesunhi@gmail.com>
Date: Wed, 19 Feb 2020 21:46:13 -0800
Subject: [PATCH] g

---
 lib/linked_list.rb       | 334 +++++++++++++++++++++++++++------------
 test/linked_list_test.rb |  64 ++++----
 2 files changed, 266 insertions(+), 132 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 8dee5e8d..d61f2992 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 +12,254 @@ 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
-
-    # 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
+  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, @head)
+  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 find if the linked list contains a node with specified value
-    # returns true if found, false otherwise
-    def search(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
+    return nil if @head.nil?
+    current = @head
+    max = current.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
+    return nil if @head == nil
+    current = @head
+    min = current.data
+    
+    until current.nil?
+      if current.data < min
+        min = current.data
+      end
+      current = current.next
     end
-
-    # method to return the min value in the linked list
-    # returns the data value and not the node
-    def find_min
-      raise NotImplementedError
+    
+    return min
+  end
+  
+  
+  # method that returns the length of the singly linked list
+  def length
+    length = 0
+    current = @head
+    
+    until current.nil?
+      length += 1
+      current = current.next
     end
-
-
-    # method that returns the length of the singly linked list
-    def length
-      raise NotImplementedError
+    
+    return length
+  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)
+    current = @head
+    
+    index.times do 
+      return nil if current.nil?
+      current = current.next
     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
+    
+    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 print all the values in the linked list
-    def visit
-      raise NotImplementedError
+  end
+  
+  # method to delete the first node found with specified value
+  def delete(value)
+    return nil if @head.nil?
+    
+    current = @head
+    
+    if current.data == value
+      @head = current.next
+      return
     end
-
-    # method to delete the first node found with specified value
-    def delete(value)
-      raise NotImplementedError
+    
+    until current.nil? || current.next.nil?
+      if current.next.data == value
+        if current.next.next == nil
+          current.next = nil
+        else
+          current.next = current.next.next
+        end
+      end
+      current = current.next
     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 reverse the singly linked list
+  # note: the nodes should be moved and not just the values in the nodes
+  def reverse
+    current = @head
+    prev = nil
+    
+    until current.nil?
+      temp = current.next
+      current.next = prev
+      prev = current
+      current = temp
     end
-
-
-    ## Advanced Exercises
-    # returns the value at the middle element in the singly linked list
-    def find_middle_value
-      raise NotImplementedError
+    
+    @head = prev
+  end
+  
+  
+  
+  ## Advanced Exercises
+  # returns the value at the middle element in the singly linked list
+  def find_middle_value
+    return nil if @head.nil?
+    
+    slow = @head
+    fast = @head.next
+    
+    until fast.nil?
+      slow = slow.next
+      fast = fast.next.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
+  
+  # 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
+    fast = @head
+    
+    return nil if fast.nil? || current.nil?
+    
+    n.times do
+      fast = fast.next
+      return nil if fast.nil?
     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
+    
+    until fast.next.nil?
+      current = current.next
+      fast = fast.next
     end
-
-
-    # Additional Exercises 
-    # returns the value in the first node
-    # returns nil if the list is empty
-    def get_first
-      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
+    return false if @head.nil? || @head.next.nil?
+    
+    fast = @head
+    slow = @head
+    
+    until fast.nil? || fast.next.nil?
+      return true if slow == fast
+      
+      fast = fast.next.next
+      slow = slow.next
     end
-
-    # method that inserts a given value as a new last node in the linked list
-    def add_last(value)
-      raise NotImplementedError
+    return false
+  end
+  
+  
+  # Additional Exercises 
+  # returns the value in the first node
+  # returns nil if the list is empty
+  def get_first
+    return nil if @head.nil?
+    
+    return @head.data
+  end
+  
+  # method that inserts a given value as a new last node in the linked list
+  def add_last(value)
+    if @head.nil?
+      add_first(value)
+      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
+    
+    current = @head
+    
+    until current.next.nil?
+      current = current.next
     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
+    
+    current.next = Node.new(value)
+    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
+    return nil if @head.nil?
+    current = @head
+    
+    until 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
-
-      # 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 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)
+    raise NotImplementedError
+  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
diff --git a/test/linked_list_test.rb b/test/linked_list_test.rb
index 22b55ef0..51ec053a 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -12,50 +12,50 @@
     before do
         @list = LinkedList.new
     end
-
+    
     describe 'initialize' do
         it 'can be created' do
-
+            
             # Assert
             expect(@list).must_be_kind_of LinkedList
         end
     end
-
+    
     describe 'add_first & get_first' do
         it 'can add values to an empty list' do
             # Act
             @list.add_first(3)
-
+            
             # Assert
             expect(@list.get_first).must_equal 3
         end
-
+        
         it 'will put the last added item to the front of the list' do
             # Act
             @list.add_first(1)
             @list.add_first(2)
-
+            
             # Assert
             expect(@list.get_first).must_equal 2
-
+            
             # Act again
             @list.add_first(3)
-
+            
             # Assert
             expect(@list.get_first).must_equal 3
         end
-
+        
         it 'will return `nil` for `getFirst` if the list is empty' do
-
+            
             expect(@list.get_first).must_be_nil
         end
     end
-
+    
     describe "length" do
         it "will return 0 for an empty list" do
             expect(@list.length).must_equal 0
         end
-
+        
         it "will return the length for nonempty lists" do
             count = 0
             while count < 5
@@ -65,54 +65,54 @@
             end
         end
     end
-
+    
     describe "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
         end
-
+        
         it "will put new items to the rear of the list" do
             @list.add_last(2)
             expect(@list.length).must_equal 1
             expect(@list.get_last).must_equal 2
-
+            
             @list.add_last(3)
             expect(@list.get_first).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_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
             expect(@list.find_min()).must_be_nil
         end
-
+        
         it 'can retrieve the max and min values in the list' do
             count = 0
             while count < 5
@@ -121,28 +121,28 @@
                 expect(@list.find_min).must_equal 0
                 count += 1
             end
-
+            
             @list.add_last(100)
             @list.add_first(-12)
             expect(@list.find_max).must_equal 100
             expect(@list.find_min).must_equal(-12)
         end
     end
-
+    
     describe "delete" do
         it "delete from empty linked list is a no-op" do
             expect(@list.length).must_equal 0
             @list.delete(4)
             expect(@list.length).must_equal 0
         end
-
+        
         it "can delete valid values from list" do
             @list.add_last(9)
             @list.add_last(10)
             @list.add_first(4)
             @list.add_first(3)
             @list.add_first(2)
-
+            
             # delete fist node (requires updating head)
             @list.delete(2)
             expect(@list.get_first).must_equal 3
@@ -150,7 +150,7 @@
             expect(@list.get_last).must_equal 10
             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
@@ -158,7 +158,7 @@
             expect(@list.get_last).must_equal 9
             expect(@list.find_max).must_equal 9
             expect(@list.find_min).must_equal 3
-
+            
             # delete fist node (requires updating head)
             @list.delete(4)
             expect(@list.get_first).must_equal 3
@@ -168,18 +168,18 @@
             expect(@list.find_min).must_equal 3
         end
     end
-
+    
     describe "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
-
+        
         it 'can retrieve an item at index n from the end in the list' do
             @list.add_first(1)
             @list.add_first(2)
             @list.add_first(3)
             @list.add_first(4)
-
+            
             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
@@ -187,7 +187,7 @@
             expect(@list.find_nth_from_end(4)).must_be_nil
         end
     end
-
+    
     describe "reverse" do
         it 'can retrieve an item at index n from the end in the list' do
             @list.add_first(4)
@@ -195,7 +195,7 @@
             @list.add_first(2)
             @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