Time - Jocelyn

lib/linked_list.rb

@@ -2,87 +2,169 @@
 # 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
+  attr_accessor :next, :previous # allow external entities to read or write next node
 
-  def initialize(value, next_node = nil)
+  def initialize(value, next_node = nil, previous_node = nil)
     @data = value
+    @previous = previous_node
     @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
+      @head = nil 
+      @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
+      current = @head
+
+      while 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
+
+      while current != nil
+        max = current.data if current.data > max
+        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
+      current = @head
+      return nil if current == nil
+
+      min = current.data
+      while current != nil
+        min = current.data if current.data < min
+        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
+      current, length = @head, 0
+
+      while 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
-    # Time Complexity: ?
-    # Space Complexity: ?
+     # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def get_at_index(index)
-      raise NotImplementedError
+      current = @head
+      current_index = 0
+
+      return nil if current == nil
+
+      while current != nil
+        return current.data if current_index == index
+        current_index += 1
+        current = current.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
+      current = @head
+
+      while current != nil
+        puts current.data
+        current = current.next
+      end
     end
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def delete(value)
-      raise NotImplementedError
+      current = @head
+
+      while current != nil
+        if current.data == value
+          if current.previous != nil
+            current.previous.next = current.next
+          else
+            @head = current.next
+            @head.previous = nil
+          end
+        end
+
+        current = 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
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def reverse
-      raise NotImplementedError
+      current = @head
+
+      while current != nil
+        temp = current.previous
+        current.previous = current.next
+        current.next = temp
+
+        current = current.previous
+      end
+
+      temp = @head
+      @head = @tail
+      @tail = temp
     end
 
 
@@ -118,7 +200,7 @@ def has_cycle
     # Time Complexity: ?
     # Space Complexity: ?
     def get_first
-      raise NotImplementedError
+      @head ? @head.data : nil
     end
 
     # method that inserts a given value as a new last node in the linked list