Time - Sharon Cheung

lib/linked_list.rb

@@ -1,88 +1,177 @@
 
-# Defines a node in the singly linked list
+# Defines a node in the doubly 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
+  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
+# Defines the doubly 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: 0(1)
+    # Space Complexity: 0(1)
     def add_first(value)
-      raise NotImplementedError
+      if @head.nil?
+        @head = @tail = Node.new(value)
+      else
+        new_node = Node.new(value)
+        new_node.next = @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?
+      current = @head
+      until current == nil
+        if current.data == value 
+          return true
+        end
+        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 = 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
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     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
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def length
-      raise NotImplementedError
+      return 0 if @head.nil?
+      count = 0
+      current = @head
+      until current == nil
+        current = current.next
+        count += 1
+      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
+      return nil if @head.nil?
+      current = @head
+      index.times do
+        if current.next.nil?
+          return nil
+        end
+        current = current.next
+      end
+      return current.data
     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
+      curernt = @head 
+      until current == nil
+        puts current.data
+        current = current.next
+      end
     end
 
     # method to delete the first node found with specified value
     # Time Complexity: ?
     # Space Complexity: ?
     def delete(value)
-      raise NotImplementedError
+      return nil if @head.nil?
+      if @head.data == value
+        @head = @head.next
+        @head.previous = nil
+      elsif @tail.data == value
+        @tail = @tail.previous
+        @tail.next = nil
+      else
+        current = @head
+        until current == nil
+          if current.data == value
+            current.previous.next = current.next
+            current.next.previous = current.previous
+          end
+          current = current.next
+        end
+      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: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def reverse
-      raise NotImplementedError
+      return nil if @head.nil?
+      current = @head
+      previous_node = nil
+
+      until current == nil
+        temp = current.previous
+        current.previous = current.next
+        current.next = temp
+        current = current.previous
+      end
+
+      if temp 
+        @head = temp.previous
+      end
     end
 
 
@@ -118,7 +207,8 @@ 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