Erika - Branches

lib/linked_list.rb

@@ -1,122 +1,275 @@
-
 # Defines a node in the singly linked list
 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
   end
+
 end
 
 # 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
+
+      new_node = Node.new(value, @head)
+      @head = new_node
+
     end
-
-    # method to find if the linked list contains a node with specified value
-    # returns true if found, false otherwise
+#     # 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
+
+      if current.data != value
+        current = current.next
+      elsif current.data == value
+        return true
+      end
+
+      return false if current.nil? || current.next.nil?
+
     end
 
-    # method to return the max value in the linked list
-    # returns the data value and not the node
+#     # method to return the max value in the linked list
+#     # returns the data value and not the node
     def find_max
-      raise NotImplementedError
+
+      max = 0 
+      current = @head
+      return nil if @head.nil?
+
+      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
+#     # 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 @head.nil?
+      min = @head.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
+#     # method that returns the length of the singly linked list
     def length
-      raise NotImplementedError
+
+      current = @head
+      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
+#     # 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
+      current_index = 0
+
+      until current_index == index
+        return nil if current.nil? 
+        current = current.next
+        current_index += 1
+      end
+
+      return current.data
+
     end
 
-    # method to print all the values in the linked list
+#     # method to print all the values in the linked list
     def visit
-      raise NotImplementedError
+
+      current = @head
+
+      until current.nil?
+        print current
+        current = current.next
+      end
+
     end
 
-    # method to delete the first node found with specified value
+#     # method to delete the first node found with specified value
     def delete(value)
-      raise NotImplementedError
+
+      current = @head
+      previous = nil 
+      return nil if current.nil?
+
+
+      until current.data == value
+        previous = current
+        current = current.next
+      end
+
+
+
+      if previous.nil?
+        @head = current.next 
+      else
+        previous.next = current.next
+      end
+
+
     end
 
-    # method to reverse the singly linked list
-    # note: the nodes should be moved and not just the values in the nodes
+#     # 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
+
+      return if @head.nil?
+
+      previous = nil
+      current = @head
+
+
+      until current.next.nil?
+
+        temp = current.next
+        current.next = previous
+        previous = current
+        current = temp
+
+      end     
+
+      current.next = previous
+      @head = current
+
     end
 
 
-    ## Advanced Exercises
-    # returns the value at the middle element in the singly linked list
+#     ## Advanced Exercises
+#     # returns the value at the middle element in the singly linked list
     def find_middle_value
-      raise NotImplementedError
+
+      mid = self.length / 2
+      self.get_at_index(mid)
+
     end
 
-    # find the nth node from the end and return its value
-    # assume indexing starts at 0 while counting to n
+#     # 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
 
-    # 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
+      return nil if @head.nil?
+
+      count = 0
+      current = @head
+      curr = @head
+
+      until current.next.nil?
+        count += 1
+        current = current.next
+      end
+
+      return nil if (count - n) < 0
+
+      until count == n
+        curr = curr.next
+        count -= 1
+      end
+
+      return curr.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
+#       raise NotImplementedError
+#     end
+
+
+#     # Additional Exercises 
+#     # returns the value in the first node
+#     # returns nil if the list is empty
 
-    # Additional Exercises 
-    # returns the value in the first node
-    # returns nil if the list is empty
     def get_first
-      raise NotImplementedError
+
+      return nil if @head.nil?
+      return @head.data if [email protected]?
+
     end
 
-    # method that inserts a given value as a new last node in the linked list
+#     # method that inserts a given value as a new last node in the linked list
     def add_last(value)
-      raise NotImplementedError
+
+      current = @head 
+
+      if current.nil?
+        @head = Node.new(value)
+        return
+      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
+#     # 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
-    end
+
+      return nil if @head.nil?
+
+      current = @head
+      current = current.next until current.next.nil?
+      return current.data
 
-    # 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
+#     # 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
 
@@ -128,4 +281,4 @@ def create_cycle
 
       current.next = @head # make the last node link to first node
     end
-end
+end