Space - Nikki V

lib/linked_list.rb

@@ -3,86 +3,185 @@
 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
+
+      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
+      return nil if @head == nil
+      max = @head.data
+      current = @head
+      until 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
+      return nil if @head == nil
+      min = @head.data
+      current = @head
+      until 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
+      return 0 if @head == nil
+
+      count = 0
+      if @head.next
+        current = @head
+        while current != nil
+          count += 1
+          current = current.next
+        end
+      else
+        current = @tail
+        while current != nil
+          count += 1
+          current = current.previous
+        end 
+      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?
+      count = 0
+      current = @head
+      while count < index
+        if current.nil?
+          return nil
+        else
+          current = current.next
+          count += 1
+        end
+      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
+      if @head.nil?
+        print "nil" 
+        return
+      else
+        current = @head
+        while current
+          print current.data
+          current = current.next
+        end
+      end
     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
+      current = @head
+      while current != nil
+        if current.data == value
+          if current.next && current.previous
+
+            previous = current.previous
+            next_node = current.next
+
+            previous.next = next_node
+            next_node.previous = previous
+
+          elsif current.previous.nil?
+            @head = current.next
+            @head.previous = nil
+          else
+            @tail = current.previous
+            @tail.next = 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
+      return nil if @head.nil?
+      current = @head
+      previous = nil
+
+      while current != nil
+        next_value = current.next  
+        current.next = previous
+        previous = current
+        current = next_value 
+      end
+
+      @head = previous
     end
 
 
@@ -96,10 +195,28 @@ 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
+      return nil if @head.nil?
+
+      value = @head
+      counter = value
+
+      n.times do 
+        if counter.next != nil 
+          counter = counter.next
+        else
+          return nil
+        end
+      end
+
+      until counter.next == nil
+        value = value.next
+        counter = counter.next
+      end
+
+      return value.data
     end
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
@@ -115,25 +232,32 @@ 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 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: ?
+    # 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, nil, @tail)
+        @tail.next = new_node
+        @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
     end
 
     # method to insert a new node with specific data value, assuming the linked