Space - Stephanie

lib/linked_list.rb

@@ -2,7 +2,7 @@
 # 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, :data # allow external entities to read or write next node
 
   def initialize(value, next_node = nil)
     @data = value
@@ -12,69 +12,154 @@ def initialize(value, next_node = nil)
 
 # Defines the singly linked list
 class LinkedList
-    def initialize
+    def initialize 
       @head = nil # keep the head private. Not accessible outside this class
     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) bc it only adds one thing regardless of how big the list is
+    # Space Complexity: O(1)
     def add_first(value)
-      raise NotImplementedError
+      if @head.nil? 
+        @head = Node.new(value)
+      else 
+        @head = Node.new(value, @head) 
+      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) because worst case it needs to run through all items in list 
+    # Space Complexity: O(1)
     def search(value)
-      raise NotImplementedError
+      return false if @head.nil? 
+
+      pointer = @head 
+
+      until pointer.nil?
+        if pointer.data == value
+          return true 
+        end 
+        pointer = pointer.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?
+
+      pointer = @head
+      max = @head.data
+
+      until 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) bc it has to run through every item 
+    # Space Complexity: O(1)
     def find_min
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      pointer = @head
+      min = @head.data
+
+      until 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) bc it has to run through every item 
+    # Space Complexity: O(1)
     def length
-      raise NotImplementedError
+      return 0 if @head.nil?
+
+      count = 1 
+      pointer = @head 
+
+      until pointer.next.nil?
+        pointer = pointer.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) could possibly have to run through every item in list
+    # Space Complexity: O(1)
     def get_at_index(index)
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      pointer = @head
+      pointer_index = 0
+      until pointer.nil?
+        if pointer_index == index
+          return pointer.data
+        end
+        pointer_index += 1
+        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) bc it has to go thru every item on the list
+    # Space Complexity: O(1)
     def visit
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      pointer = @head 
+
+      until 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) because you could look through entire list before you found specified value
+    # Space Complexity: O(1)
     def delete(value)
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      pointer = @head
+      prev_node = nil 
+
+      until pointer.nil?
+        if pointer.data == value 
+          if prev_node
+            prev_node.next = pointer.next
+          else
+            @head = pointer.next
+          end
+          return
+        else  
+          prev_node = pointer 
+          pointer = pointer.next
+        end
+      end
     end
 
     # method to reverse the singly linked list
@@ -118,22 +203,41 @@ def has_cycle
     # Time Complexity: ?
     # Space Complexity: ?
     def get_first
-      raise NotImplementedError
+      return nil if @head.nil? 
+
+      return @head.value 
     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
+      if @head.nil? 
+        @head = Node.new(value)
+        return
+      end
+
+      pointer = @head
+
+      until pointer.next.nil? 
+        pointer = pointer.next
+      end
+      pointer.next = Node.new(value)
     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
+      return nil if @head.nil?
+      pointer = @head
+
+      until pointer.next.nil?
+        pointer = pointer.next 
+      end
+
+      return pointer.data
     end
 
     # method to insert a new node with specific data value, assuming the linked

test/linked_list_test.rb

@@ -63,14 +63,14 @@
         end
 
         it "returns false if the element is not in the list" do
-          @list = LinkedList.new
-          @list.add_first(3)
-          @list.add_first(2)
-          expect(@list.search("pasta")).must_equal false
+            @list = LinkedList.new
+            @list.add_first(3)
+            @list.add_first(2)
+            expect(@list.search("pasta")).must_equal false
         end
 
         it "returns false for an empty list" do
-          expect(@list.search(3)).must_equal false
+            expect(@list.search(3)).must_equal false
         end
     end
 
@@ -107,7 +107,7 @@
         end
     end
 
-    xdescribe "Optional addLast & getLast" do
+    describe "Optional addLast & getLast" do
         it "will add to the front if the list is empty" do
             @list.add_last(1)
             expect(@list.get_at_index(0)).must_equal 1
@@ -211,7 +211,7 @@
         end
     end
 
-    describe "reverse" do
+    xdescribe "reverse" do
         it 'can retrieve an item at index n from the end in the list' do
             @list.add_first(4)
             @list.add_first(3)