Alicia - Time

lib/linked_list.rb

@@ -3,10 +3,12 @@
 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, prev_node = nil)
     @data = value
     @next = next_node
+    @previous = prev_node
   end
 end
 
@@ -18,71 +20,185 @@ 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
-    # 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)
+        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
+      current_node = @head
+
+      until current_node.nil?
+        return true if current_node.data == value
+
+        current_node = current_node.next
+      end
+
+      return false
     end
 
     # method to return the max value in the linked list
     # returns the data value and not the node
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_max
-      raise NotImplementedError
+      current_node = @head
+      max_value = current_node.data unless current_node.nil?
+
+      until current_node.nil?
+        max_value = current_node.data if current_node.data > max_value
+
+        current_node = current_node.next
+      end
+
+      return max_value
     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_node = @head
+      min_value = current_node.data unless current_node.nil?
+
+      until current_node.nil?
+        min_value = current_node.data if current_node.data < min_value
+
+        current_node = current_node.next
+      end
+
+      return min_value
     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_node = @head
+      length = 0
+
+      until current_node.nil?
+        length += 1
+
+        current_node = current_node.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
+      length = self.length
+      return nil if length <= index
+      return @head.data if index == 0
+
+      current_index = 0
+      current_node = @head
+
+      until current_index == index
+        current_index += 1
+        current_node = current_node.next
+      end
+
+      return current_node.data
     end
 
     # method to print all the values in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(n)
     def visit
-      raise NotImplementedError
+      return nil if @head.nil?
+      current_node = @head
+
+      until current_node.nil?
+        puts current_node.data
+
+        current_node = current_node.next
+      end
+
+      return
     end
 
     # method to delete the first node found with specified value
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def delete(value)
-      raise NotImplementedError
+      return if @head.nil?
+
+      if @head.data == value
+        @head = nil if @head.next.nil?
+        @head = @head.next unless @head.nil?
+        return
+      end
+
+      current_node = @head
+      previous_node = @head.previous
+
+      until current_node.nil?
+        if current_node.next.nil?
+          @tail = previous_node
+          previous_node.next = nil
+          return 
+        end
+
+        next_node = current_node.next
+
+        if current_node.data == value
+
+          next_node.previous = previous_node
+          previous_node.next = next_node
+          @tail = next_node if next_node.next.nil?
+          return
+        end
+
+        previous_node = current_node
+        current_node = current_node.next
+      end
+
+      return
     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()
+    # Space Complexity: O(n)
     def reverse
-      raise NotImplementedError
+      return if @head.nil?
+      return if @head.next.nil?
+
+      temp = @head
+      @head = temp
+      @tail = @head
+
+      current = @head
+
+      until current == nil
+        temp = current.next
+        current.next = current.previous
+        current.previous = temp
+
+        current = current.previous
+      end
+
+      return
     end
 
 
@@ -96,10 +212,23 @@ 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
+      length = self.length
+      return nil if length <= n
+      return @head.data if n == 0
+      return @tail.data if n == length - 1
+
+      current_index = length - 1
+      current_node = @tail
+
+      until current_index == n
+        current_index -= 1
+        current_node = current_node.previous
+      end
+
+      return current_node.data
     end
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
@@ -115,25 +244,32 @@ def has_cycle
     # Additional Exercises 
     # returns the value in the first node
     # returns nil if the list is empty
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def get_first
-      raise NotImplementedError
+      return @head.data unless @head.nil?
     end
 
     # method that inserts a given value as a new last node in the linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def add_last(value)
-      raise NotImplementedError
+      if @head.nil?
+        @head = @tail = Node.new(value)
+      else
+        new_node = Node.new(value)
+        @tail.next = new_node
+        new_node.previous = @tail
+        @tail = new_node
+      end
     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: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def get_last
-      raise NotImplementedError
+      return @tail.data unless @tail.nil?
     end
 
     # method to insert a new node with specific data value, assuming the linked