From e92720b01060caa8903ac5db5c659076b0a322d6 Mon Sep 17 00:00:00 2001
From: Jessica <jessica.homet@gmail.com>
Date: Mon, 26 Aug 2019 00:23:39 -0700
Subject: [PATCH] implement methods

---
 lib/linked_list.rb       | 352 ++++++++++++++++++++++++++-------------
 test/linked_list_test.rb |   9 +-
 2 files changed, 245 insertions(+), 116 deletions(-)

diff --git a/lib/linked_list.rb b/lib/linked_list.rb
index 501c60fb..fd7f0398 100644
--- a/lib/linked_list.rb
+++ b/lib/linked_list.rb
@@ -12,152 +12,276 @@ 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: O(1)
+  # Space Complexity O(1)
+  def add_first(value)
+    @head = Node.new(value, @head) # i don't fully understand why next_node is @head
 
-    # 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
+    return @head.data
+  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
-    end
+  # method to find if the linked list contains a node with specified value
+  # returns true if found, false otherwise
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1)
+  def search(value)
+    current = @head
 
-    # 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
+    while current
+      return true if current.data == value
+      current = current.next
     end
 
+    return false
+  end
 
-    # method that returns the length of the singly linked list
-    # Time Complexity:  
-    # Space Complexity
-    def length
-      raise NotImplementedError
-    end
+  # method to return the max value in the linked list
+  # returns the data value and not the node
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1)
+  def find_max
+    current = @head
 
-    # 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
+    return nil unless current
 
-    # method to print all the values in the linked list
-    # Time Complexity:  
-    # Space Complexity
-    def visit
-      raise NotImplementedError
-    end
+    max_value = current.data
 
-    # method to delete the first node found with specified value
-    # Time Complexity:  
-    # Space Complexity
-    def delete(value)
-      raise NotImplementedError
+    while current
+      max_value = current.data > max_value ? current.data : max_value
+      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
-    # Time Complexity:  
-    # Space Complexity
-    def reverse
-      raise NotImplementedError
-    end
+    return max_value
+  end
 
+  # method to return the min value in the linked list
+  # returns the data value and not the node
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1)
+  def find_min
+    current = @head
 
-    ## Advanced Exercises
-    # returns the value at the middle element in the singly linked list
-    # Time Complexity:  
-    # Space Complexity
-    def find_middle_value
-      raise NotImplementedError
+    return nil unless current
+
+    min_value = current.data
+
+    while current
+      min_value = current.data < min_value ? current.data : min_value
+      current = current.next
     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
+    return min_value
+  end
+
+  # method that returns the length of the singly linked list
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1)
+  def length
+    return 0 unless @head
+
+    length = 0
+
+    current = @head
+    while current
+      current = current.next
+      length += 1
     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
+    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
+  # Time Complexity: O(n), where n is the value of the index
+  # Space Complexity: O(1)
+  def get_at_index(index)
+    return nil unless @head
+
+    current = @head
+    
+    index.times do
+      current = current.next
+
+      return nil unless current
     end
 
+    return current.data
+  end
+
+  # method to print all the values in the linked list
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1), unless printing takes space?
+  def visit
+    return nil unless @head
 
-    # 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
+    current = @head
+
+    while current
+      puts current.data
+      current = current.next
     end
+  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
+  # method to delete the first node found with specified value
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1)
+  def delete(value)
+    # if the value doesn't exist, just return the list
+    return self unless self.search(value)
+
+    # delete the value if at the head
+    if @head.data == value
+      @head = @head.next ? @head.next : nil
+      return
     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
+    # delete value somewhere else
+    previous = @head
+    current = @head.next
+    while current
+      if current.data == value
+        previous.next = current.next ? current.next : nil
+      end
+      current = current.next
+      previous = previous.next
     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
+    return self
+  end
+
+  # method to reverse the singly linked list
+  # note: the nodes should be moved and not just the values in the nodes
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1)?
+  def reverse
+    return nil unless @head
+    return self if self.length < 2
+
+    temporary = nil
+    previous = nil
+    current = @head
+    puts self.visit
+
+    # printing things to try to trace what's happening
+    while current
+      puts "------------"
+      puts "temporary: #{temporary.data if temporary}"
+      puts "previous: #{previous.data if previous}"
+      puts "current: #{current.data}"
+      puts "next: #{current.next.data if current.next}"
+      puts "list: #{self.visit}"
+      temporary = current.next
+      current.next = previous
+      previous = current
+      current = temporary
+
+      # puts "temporary: #{temporary.data if temporary}"
+      # puts "previous: #{previous.data}"
+      # puts "current: #{current.data if current}"
+      # puts "next: #{current.next.data if current && current.next}"
     end
+    
+    @head = previous
+
+    puts self.visit
+    return self
+  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
+
+  # find the nth node from the end and return its value
+  # assume indexing starts at 0 while counting to n
+  # Time Complexity: O(n-m), where n is the length of the list and m is the index
+  # Space Complexity: O(1)
+  def find_nth_from_end(n)
+    return nil if self.length - 1 < n
+
+    self.get_at_index(self.length - 1 - n)
+  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
+  # 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: O(1)
+  # Space Complexity: O(1)
+  def get_first
+    return @head ? @head.data : nil
+  end
 
-      # navigate to last node
+  # method that inserts a given value as a new last node in the linked list
+  # Time Complexity: O(n), where n is the length of the list
+  # Space Complexity: O(1)
+  def add_last(value)
+    if @head
       current = @head
-      while current.next != nil
-          current = current.next
+
+      while current.next
+        current = current.next
       end
 
-      current.next = @head # make the last node link to first node
+      return current.next = Node.new(value)
+    else
+      self.add_first(value)
+
+      return @head
+    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: O(n), where n is the length of the list
+  # Space Complexity: O(1)
+  def get_last
+    return nil unless @head
+
+    current = @head
+    current = current.next while current.next
+
+    return current.data
+  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
+
+  # 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 8311c439..86338027 100644
--- a/test/linked_list_test.rb
+++ b/test/linked_list_test.rb
@@ -96,6 +96,11 @@
             expect(@list.get_last).must_equal 4
             expect(@list.length).must_equal 3
         end
+
+        it "will return `nil` for `get_last` if the list is empty" do
+            # Act-Assert
+            expect(@list.get_last).must_be_nil
+        end
     end
 
     describe 'get_at_index' do
@@ -137,7 +142,7 @@
             end
             @list.add_last(100)
             @list.add_first(-12)
-            
+
             # Act-Assert
             expect(@list.find_max).must_equal 100
             expect(@list.find_min).must_equal(-12)
@@ -172,7 +177,7 @@
             expect(@list.get_last).must_equal 10
             expect(@list.find_max).must_equal 10
             expect(@list.find_min).must_equal 3
-            
+                        
             # Act (again)
             # delete last node
             @list.delete(10)