Branches - Farah

lib/linked_list.rb

@@ -19,54 +19,142 @@ 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
+      new_node = Node.new(value)
+      new_node.next = @head
+      @head = new_node
+
+      # @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
+      return nil if @head.nil?
+
+      current = @head
+      max = 0
+      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
+      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
+
+      return min
     end
 
 
     # method that returns the length of the singly linked list
-    def length
-      raise NotImplementedError
+    def length      
+      current = @head
+      counter = 0
+      until current.nil?
+        counter += 1
+        current = current.next
+      end
+
+      return counter
     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
+      # raise NotImplementedError
+      length = self.length
+      if index > length
+        return nil
+      end
+
+      current = @head
+
+      index.times do 
+        current = current.next
+      end
+
+      return current.data
     end
 
     # method to print all the values in the linked list
     def visit
-      raise NotImplementedError
+      length = self.length
+      values = []
+
+      current = @head
+      length.time do
+        values << current.data
+        current = current.next
+      end
     end
 
     # 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
+        return nil if current.nil?
+        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
     def reverse
-      raise NotImplementedError
+      return if @head.nil?
+
+      current = @head
+      previous = nil
+
+      until current.next.nil?
+        temp = current.next
+        current.next = previous
+        previous = current
+        current = temp
+      end
+
+      current.next = previous
+      @head = current
     end
 
 
@@ -79,39 +167,106 @@ def find_middle_value
     # 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
+      return nil if @head.nil?
+
+      current = @head
+      n_ahead = @head
+
+      n.times do
+        return if n_ahead.next.nil?
+        n_ahead = n_ahead.next
+      end
+
+      until n_ahead.next.nil?
+        current = current.next
+        n_ahead = n_ahead.next
+      end
+
+      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
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      fast = @head
+      slow = @head
+
+      until fast.nil? || fast.next.nil?
+        fast = fast.next.next
+        slow = slow.next
+        if fast == slow
+          return true
+        end
+      end
+      return false
     end
 
 
     # Additional Exercises 
     # returns the value in the first node
     # returns nil if the list is empty
     def get_first
-      raise NotImplementedError
+      # raise NotImplementedError
+      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)
-      raise NotImplementedError
+      # raise NotImplementedError
+      # length = self.length
+      new_node = Node.new(value)
+
+      current = @head
+      if current.nil?
+        return @head = new_node
+      end
+
+      until current.next.nil?
+        current = current.next
+      end
+
+      current.next = new_node
     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
+      # raise NotImplementedError
+      # length = self.length
+
+      return nil if @head.nil?
+
+      current = @head
+      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
+      return nil if @head.nil?
+
+      current = @head
+
+      until current.nil?
+        if value > current.data && value <= current.next.data
+          new_node = Node.new(value, current.next)
+          current.next = new_node
+          return
+        else
+          current = current.next
+        end
+      end
+
+      return current = Node.new(value)
     end
 
     # Helper method for tests