Yaz - Linked List

lib/linked_list.rb

@@ -12,150 +12,264 @@ 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 self 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
+  # 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)
+    if @head
+      second = @head
+      @head = Node.new(value, second)
+    else
+      @head = Node.new(value)
     end
+  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: O(n)
+  # Space Complexity: O(1)
+  def search(value)
+    if @head == nil
+      return false
     end
+    return search_help(value) != nil
+  end
 
-    # method to return the max value in the linked list
-    # returns the data value and not the node
-    def find_max
-      raise NotImplementedError
+  # 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
+    max = @head.data
+    current = @head
+    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
-    # Time Complexity: ?
-    # Space Complexity: ?
-    def find_min
-      raise NotImplementedError
+  # method to return the min value in the linked list
+  # returns the data value and not the node
+  # Time Complexity: O(n)
+  # Space Complexity: O(1)
+  def find_min
+    if @head == nil
+      return nil
     end
+    min = @head.data
+    current = @head
+    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
-    # Time Complexity: ?
-    # Space Complexity: ?
-    def length
-      raise NotImplementedError
+  # method that returns the length of the singly linked list
+  # Time Complexity: O(n)
+  # Space Complexity: O(1)
+  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
-    # Time Complexity: ?
-    # Space Complexity: ?
-    def get_at_index(index)
-      raise NotImplementedError
+    current = @head
+    length = 0
+    while current != nil
+      length += 1
+      current = current.next
     end
+    return length
+  end
 
-    # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
-    def visit
-      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: O(n)
+  # Space Complexity: O(1)
+  def get_at_index(index)
+    node = get_node_at_index(index)
+    if node
+      return node.data
+    else
+      return nil
     end
+  end
 
-    # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
-    def delete(value)
-      raise NotImplementedError
+  # method to print all the values in the linked list
+  # Time Complexity: O(n)
+  # Space Complexity: O(1)
+  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: O(n)
+  # Space Complexity: O(1)
+  def delete(value)
+    target = search_help(value)
+    after_target = target.next
+    target.next = nil
+    before_target_index = self.length - 2
+    before_target = get_node_at_index(before_target_index)
+    before_target.next = after_target
+  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 reverse the singly linked list
+  # note: the nodes should be moved and not just the values in the nodes
+  # Time Complexity: O(n)
+  # Space Complexity: O(n)
+  def reverse
+    new_list = LinkedList.new
+    current = @head
+    while current != nil
+      new_list.add_first(current)
+      current = current.next
     end
+    @head.next = nil
+    @head = new_list.get_first
+  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
+  ## Advanced Exercises
+  # returns the value at the middle element in the singly linked list
+  # Time Complexity: O(n)
+  # Space Complexity: O(1)
+  def find_middle_value
+    length = self.length
+    middle_index = length/2
+    return get_at_index(middle_index)
+  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
+  # find the nth node from the end and return its value
+  # assume indexing starts at 0 while counting to n
+  # Time Complexity: O(n)
+  # Space Complexity: O(1)
+  def find_nth_from_end(n)
+    length = self.length
+    nth_from_end_index = length - 1 - n
+    return get_at_index(nth_from_end_index)
+  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
+  # 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
+    current = @head
+    seen_nodes = []
+    # while current != nil || has_node?(current)
+    #   current = current.next
+    #   if current == nil
+    #     return false
+    #   end
+    #   if has_node
+    # end
+  end
+  def has_node?(array, node)
+    array.each do |current_node|
+      if current_node == node
+        return true
+      end
     end
+    return false
+  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
+      return @head
+    else
+      return nil
     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
-    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 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
+
+  # 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
+    # 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
+  end
 
-      # navigate to last node
-      current = @head
-      while current.next != nil
-          current = current.next
+  private
+
+  def get_node_at_index(index)
+    length = self.length
+    if length < index
+      return nil
+    end
+    current = @head
+    (0..(length-1)).each do |i|
+      if i == index
+        return current
       end
+      current = current.next
+    end
+    return nil
+  end
 
-      current.next = @head # make the last node link to first node
+  def search_help(value)
+    current = @head
+    while current != nil
+      if current.data == value
+        return current
+      else
+        current = current.next
+      end
     end
+    return nil
+  end
+
 end