Earth - Kal

lib/linked_list.rb

@@ -18,95 +18,195 @@ 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_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
     def find_max
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      current_node = @head
+      max = 0
+      until current_node.nil?
+        if current_node.data > max
+          max = current_node.data
+        end
+        current_node = current_node.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?
+
+      current_node = @head
+      min = current_node.data
+
+      until current_node.nil?
+        if current_node.data < min
+          min = current_node.data
+        end
+        current_node = current_node.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 nil if @head.nil?   # I don't understand why this is not passing the test
+
+      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(n)
+    # Space Complexity: O(1)
     def add_last(value)
-      raise NotImplementedError
+      new_node = Node.new(value)
+
+      current_node = @head
+      if current_node.nil?
+        return @head = new_node
+      end
+
+      until current_node.next.nil?
+        current_node = current_node.next
+      end
+
+      current_node.next = new_node
     end
 
     # method that returns the length of the singly linked list
-    # Time Complexity: ?
-    # Space Complexity: ?
+    # Time Complexity: O(1)
+    # Space Complexity: O(1)
     def length
-      raise NotImplementedError
+      current_node = @head
+      counter = 0
+      until current_node.nil?
+        counter += 1
+        current_node = current_node.next
+      end
+
+      return counter
     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 index > length
+
+      current_node = @head
+
+      index.times do 
+        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(1)
     def visit
-      raise NotImplementedError
+      current_node = @head
+
+      return nil if current_node.nil?
+      until current_node.nil?
+        puts current_node.data
+        current_node = current_node.next
+      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 nil if @head.nil?
+      current_node = @head
+      previous = nil
+
+      until current_node.nil?
+        if current_node.data == value
+          # previous.next = current.next
+          if previous == nil
+            @head = current_node.next
+          else
+            previous.next = current_node.next
+          end
+        end
+        previous = current_node
+        current_node = current_node.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_node = @head
+      previous = nil
+
+      until current_node.next.nil?
+        temp = current_node.next
+        current_node.next = previous
+        previous = current_node
+        current_node = temp
+      end
+
+      current_node.next = previous
+      @head = current_node
     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?
+
+      current_node = @head
+      until current_node.next == nil
+        current_node = current_node.next
+      end
+
+      return current_node.data
     end
 
     ## Advanced Exercises
@@ -122,7 +222,22 @@ def find_middle_value
     # Time Complexity: ?
     # Space Complexity: ?
     def find_nth_from_end(n)
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      current_node = @head
+      n_ahead = @head
+
+      n.times do
+        return if n_ahead.next.nil?
+        n_ahead = n_ahead.next
+      end
+
+      until n_ahead.next.nil?
+        current_node = current_node.next
+        n_ahead = n_ahead.next
+      end
+
+      return current_node.data
     end
 
     # checks if the linked list has a cycle. A cycle exists if any node in the
@@ -131,15 +246,40 @@ def find_nth_from_end(n)
     # Time Complexity: ?
     # Space Complexity: ?
     def has_cycle
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      fast = @head
+      slow = @head
+
+      until fast.nil? || fast.next.nil?
+        fast = fast.next.next
+        slow = slow.next
+        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: ?
     def insert_ascending(value)
-      raise NotImplementedError
+      return nil if @head.nil?
+
+      current_node = @head
+
+      until current_node.nil?
+        if value > current_node.data && value <= current_node.next.data
+          new_node = Node.new(value, current_node.next)
+          current_node.next = new_node
+          return
+        else
+          current_node = current_node.next
+        end
+      end
+
+      return current_node = Node.new(value)
     end
 
     # Helper method for tests