Earth - Beauttie

lib/linked_list.rb

@@ -18,128 +18,267 @@ 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
+      @head = Node.new(value, @head)
     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
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_max
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      max = @head.data
+      current = @head
+      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
+      return nil if @head.nil?
+
+      min = @head.data
+      current = @head
+      while current != nil
+        min = current.data if current.data < min
+        current = current.next
+      end
+
+      return min
     end
 
 
     # 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.nil? ? nil : @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(n)
+    # Space Complexity: O(1)
     def add_last(value)
-      raise NotImplementedError
+      if @head.nil?
+        @head = Node.new(value)
+      else
+        current = @head
+        until current.next.nil?
+          current = current.next
+        end
+
+        current.next = Node.new(value)
+      end  
     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
+      count = 0
+      current = @head
+      while current != nil
+        count += 1
+        current = current.next
+      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
+        return nil if current.nil?
+
+        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
+      return nil if @head.nil?
+
+      current = @head
+      while current != nil
+        print current.data
+      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
+      return if @head.nil?
+
+      if @head.data == value
+        @head = @head.next
+        return
+      end
+
+      current = @head
+      until current.next.nil?
+        if current.next.data == value
+          current.next = current.next.next
+          return
+        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 if @head.nil? || @head.next.nil?
+
+      current = @head
+      previous = nil
+      until current.nil?
+        temp = current.next
+        current.next = previous
+        previous = current
+        current = temp
+      end
+
+      @head = previous
     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(n)
+    # Space Complexity: O(1)
     def get_last
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      current = @head
+      until current.next.nil?
+        current = current.next
+      end
+
+      return current.data
     end
 
     ## Advanced Exercises
     # returns the value at the middle element in the singly linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def find_middle_value
-      raise NotImplementedError
+      if @head.nil?
+        return nil
+      else
+        slow = @head
+        fast = @head.next
+        while fast != nil
+          slow = slow.next
+          fast = fast.next
+          fast = fast.next if fast != nil
+        end
+
+        return slow
+      end
     end
 
     # 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?
+
+      current = @head
+      n.times do
+        current = current.next
+        return nil if current.nil?
+      end
+
+      trailing_current = @head
+      until current.next.nil?
+        current = current.next
+        trailing_current = trailing_current.next
+      end
+
+      return trailing_current.data
     end
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
     # linked list links to a node already visited.
     # returns true if a cycle is found, false otherwise.
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def has_cycle
-      raise NotImplementedError
+      if @head.nil? || @head.next.nil?
+        return false
+      end
+
+      slow = @head
+      fast = @head
+      while fast != nil
+        slow = slow.next
+        fast = fast.next
+        fast = fast.next if fast != nil
+
+        return true if fast == slow
+      end
+
+      return false
     end
 
     # method to insert a new node with specific data value, assuming the linked
     # list is sorted in ascending order
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(n)
+    # Space Complexity: O(1)
     def insert_ascending(value)
-      raise NotImplementedError
+      if @head.nil?
+        @head = Node.new(value)
+        return
+      end
+
+      current = @head
+      while current.next != nil && current.next.data > value
+        current = current.next
+      end
+
+      current.next = Node.new(value, current.next)
     end
 
     # Helper method for tests

test/linked_list_test.rb

@@ -103,7 +103,7 @@
         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
@@ -209,7 +209,7 @@
         end
     end
 
-    xdescribe "Optional:  nth_from_the_end" do
+    describe "Optional:  nth_from_the_end" do
         it 'returns nil if n is outside the bounds of the list' do
             expect(@list.find_nth_from_end(3)).must_be_nil
         end