Time - Vicki

lib/linked_list.rb

@@ -3,86 +3,189 @@
 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
+  attr_accessor :previous 
 
-  def initialize(value, next_node = nil)
+  def initialize(value, next_node = nil, previous = nil )
     @data = value
     @next = next_node
+    @previous = previous
   end
 end
 
 # Defines the singly linked list
 class LinkedList
     def initialize
       @head = nil # keep the head private. Not accessible outside this class
+      @tail = nil 
     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: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def add_first(value)
-      raise NotImplementedError
+      if @head.nil? 
+        @head = @tail = Node.new(value)
+      else
+        new_node = Node.new(value,@head)
+        @head.previous = new_node 
+        @head = new_node  
+      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: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def search(value)
-      raise NotImplementedError
+      return false if @head.nil? 
+      pointer = @head 
+
+      until pointer.next.nil?
+
+        if pointer.data == value || pointer.next.data == value 
+          return true 
+        else  
+          pointer = pointer.next 
+        end 
+
+      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? 
+      max = @head.data
+      pointer = @head
+
+      while !pointer.nil?
+        if pointer.data > max 
+          max = pointer.data 
+        end 
+        pointer = pointer.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: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_min
-      raise NotImplementedError
+      return nil if @head.nil? 
+
+      min = @head.data
+
+      pointer = @head
+      while !pointer.nil?
+        if pointer.data < min
+          min = pointer.data 
+        end 
+        pointer = pointer.next 
+      end 
+
+      return min 
     end
 
 
     # method that returns the length of the singly linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def length
-      raise NotImplementedError
+      count = 1 
+      return 0 if @head.nil? 
+      pointer = @head
+      until pointer.next.nil? 
+        count += 1 
+        pointer = pointer.next
+      end 
+      return count 
     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: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def get_at_index(index)
-      raise NotImplementedError
+      node_index = 0 
+      pointer = @head 
+      until pointer.nil? 
+       if node_index == index 
+        return pointer.data 
+       else 
+        node_index += 1 
+       end 
+       pointer = pointer.next 
+      end 
+
+      return nil 
     end
 
     # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def visit
-      raise NotImplementedError
+      pointer = @head 
+      while !pointer.nil? 
+        puts pointer.data 
+        pointer = pointer.next 
+      end 
     end
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(n)
+
     def delete(value)
-      raise NotImplementedError
+      return nil if @head.nil? 
+      pointer = @head 
+
+
+      while !pointer.nil? 
+       if pointer.data == value 
+        if pointer == @head 
+          @head = pointer.next 
+        end 
+
+        if pointer == @tail
+          @tail = pointer.previous
+        end 
+
+        if !pointer.next.nil?
+          pointer.next.previous = pointer.previous
+        end 
+
+        if !pointer.previous.nil?
+          pointer.previous.next = pointer.next 
+        end 
+        return
+       end 
+
+       pointer = pointer.next
+      end 
+
     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
+      pointer = @head 
+
+      while !pointer.nil?
+        temp = pointer.previous
+        pointer.previous = pointer.next 
+        pointer.next = temp 
+        pointer = pointer.previous
+      end 
+        temp = @head
+        @head = @tail
+        @tail = temp
     end
 
 
@@ -96,10 +199,26 @@ def find_middle_value
 
     # find the nth node from the end and return its value
     # assume indexing starts at 0 while counting to n
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_nth_from_end(n)
-      raise NotImplementedError
+      node_index = 0
+      pointer = @tail 
+
+      until pointer == @head 
+       if node_index == n 
+        return pointer.data 
+       else 
+        node_index += 1 
+       end 
+       pointer = pointer.previous 
+      end 
+
+      if pointer == @head && (node_index  == n )
+        return @head.data
+      end 
+
+      return nil 
     end
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
@@ -118,22 +237,44 @@ def has_cycle
     # Time Complexity: ?
     # Space Complexity: ?
     def get_first
-      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
     # Time Complexity: ?
     # Space Complexity: ?
     def add_last(value)
-      raise NotImplementedError
+
+      temp = Node.new(value)
+      if @head.nil?
+        @head = @tail = temp
+        return 
+      end 
+
+      current = @head 
+      until current.next.nil? 
+        current = current.next 
+      end 
+
+      current.next = temp
+      temp.previous = current
+      @tail = temp
     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
+
+      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