Leaves - Mariya

lib/linked_list.rb

@@ -19,67 +19,190 @@ 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
     def add_first(value)
-      raise NotImplementedError
+        @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)
-      raise NotImplementedError
+      current = @head 
+      until current.nil?
+        return true if current.data == value
+        current = current.next
+      end
+
+      return false
     end
 
     # method to return the max value in the linked list
     # returns the data value and not the node
     def find_max
-      raise NotImplementedError
+      current = @head
+      return nil if current.nil?
+      max = current.data
+
+      until 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
     def find_min
-      raise NotImplementedError
+      current = @head
+      return nil if current.nil?
+      min = current.data
+
+      until 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
     def length
-      raise NotImplementedError
+      current = @head
+      return 0 if current.nil?
+      length = 0
+
+      until current.nil?
+        length += 1
+        current = current.next 
+      end 
+      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)
-      raise NotImplementedError
+      current = @head 
+      length = 0
+
+      until current.nil? 
+        length += 1
+        current = current.next
+      end
+
+      return nil if length < index 
+
+      current = @head 
+      index_value = current.data
+
+      (index + 1).times do 
+        index_value = current.data
+        current = current.next
+      end
+
+      return index_value
     end
 
     # method to print all the values in the linked list
     def visit
-      raise NotImplementedError
+      current = @head
+      return nil if head.nil?
+
+      until current.nil?
+        p current.data
+      end
+
     end
 
     # method to delete the first node found with specified value
     def delete(value)
-      raise NotImplementedError
+      return nil if @head.nil?
+      current = @head
+
+      if current.data == value 
+        return @head = current.next 
+      end
+
+      previous = nil
+      continuing_node = nil
+
+      until current.next.nil? || current.next.data == value 
+        current = current.next
+      end
+
+      return nil if current.next.nil? 
+      previous = current 
+      continuing_node = previous.next.next
+      previous.next = continuing_node
+
     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
+      previous = nil 
+      current = @head 
+      return nil if current.nil? 
+      next_node = current.next
+      current.next = nil
+
+
+      until next_node.nil?
+        previous = current
+        current = next_node
+        next_node = current.next 
+        current.next = previous
+      end
+
+      @head = current
+
     end
 
 
     ## Advanced Exercises
     # returns the value at the middle element in the singly linked list
     def find_middle_value
-      raise NotImplementedError
+      current = @head
+      temp = current
+      length = 0
+
+      until current.nil?
+        length += 1
+        temp = temp.next
+      end
+
+      middle_node = nil
+      (length / 2).times do 
+        middle_node = current.data
+        current = current.next
+      end
+
+      return middle_node
     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
+      nth_node = nil 
+      current = @head
+      temp = @head 
+      length = 0
+
+      until temp.nil?
+        length += 1
+        temp = temp.next
+      end
+
+      (length - n).times do 
+        nth_node = current.data 
+        current = current.next
+      end
+
+      return nth_node
     end
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
@@ -94,24 +217,44 @@ def has_cycle
     # returns the value in the first node
     # returns nil if the list is empty
     def get_first
-      raise NotImplementedError
+      current = @head 
+      return nil if current.nil?
+      return current.data
     end
 
     # method that inserts a given value as a new last node in the linked list
     def add_last(value)
-      raise NotImplementedError
+      if !@head 
+        @head = Node.new(value)
+        return @head
+      else
+        current = @head
+      end 
+
+      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
-      raise NotImplementedError
+      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)
-      raise NotImplementedError
     end
 
     # Helper method for tests