Aurora Anderson Linked List #17

auroralemieux · 2017-09-06T03:29:47Z

Linked Lists

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Comprehension Questions

What is the time and space complexity for each method you implemented? Provide justification.

Question	Answer
What is the time complexity of the insert method? Provide justification.	constant -- no need to visit all, just head.
What is the space complexity of the insert method? Provide justification.	constant -- no data structures, just the new node.
What is the time complexity of the search method? Provide justification.	O(n) -- at worst visiting all nodes in linked list.
What is the space complexity of the search method? Provide justification.	constant -- no new data structures needed.
What is the time complexity of the find_max method? Provide justification.	O(n) - visiting all at worst.
What is the space complexity of the find_max method? Provide justification.	constant -- no new structures
What is the time complexity of the find_min method? Provide justification.	O(n) -- visiting all at worst
What is the space complexity of the find_min method? Provide justification.	constant -- no new structures
What is the time complexity of the length method? Provide justification.	O(n) -- counting all nodes.
What is the space complexity of the length method? Provide justification.	no data structures, just a variable, so constant
What is the time complexity of the find_nth_from_beginning method? Provide justification.	O(n) as potentially visiting all nodes
What is the space complexity of the find_nth_from_beginning method? Provide justification.	constant -- no new data structures
What is the time complexity of the insert_ascending method? Provide justification.	O(n) in case of inserting at end
What is the space complexity of the insert_ascending method? Provide justification.	constant as only variables needed
What is the time complexity of the visit method? Provide justification.	O(n) printing each node
What is the space complexity of the visit method? Provide justification.	constant -- no new data structures needed
What is the time complexity of the delete method? Provide justification.	O(n) as potentially visiting all before finding target value
What is the space complexity of the delete method? Provide justification.	constant -- no new data structures
What is the time complexity of the reverse method? Provide justification.	O(n) as visiting each node
What is the space complexity of the reverse method? Provide justification.	constant even though multiple variables, as they are reassigned and no complex data structures needed
What is the time complexity of the find_middle_value method? Provide justification.	this is O(n) although technically worst case 2(O(n)) -- but constants don't matter
What is the space complexity of the find_middle_value method? Provide justification.	constant because no complex data structures
What is the time complexity of the find_nth_from_end method? Provide justification.
What is the space complexity of the find_nth_from_end method? Provide justification.
What is the time complexity of the has_cycle method? Provide justification.
What is the space complexity of the has_cycle method? Provide justification.

shrutivanw · 2017-10-31T21:47:24Z

linked_list.rb

@@ -42,17 +42,41 @@ def search(value)
  # method to return the max value in the linked list
  # returns the data value and not the node
  def find_max
-    puts "Not implemented"
+    current = @head
+    max = current.data


Check to ensure that head is not nil before accessing data. In other words, update your method to work for empty linked list scenario.

shrutivanw · 2017-10-31T21:48:16Z

linked_list.rb

  end

  # method to return the min value in the linked list
  # returns the data value and not the node
  def find_min
+    current = @head
+    min = current.data


Same as with find_max, check for null before accessing member variables in the node.

shrutivanw · 2017-10-31T21:49:23Z

linked_list.rb

    puts "Not implemented"
  end

  # method that returns the length of the singly linked list
  def length
+    counter = 1
+    current = @head
+    while current.next


Always check for null. :-) What if the linked list is empty? In that case, the length returned should be 0.

shrutivanw · 2017-10-31T21:51:23Z

linked_list.rb

+    index = 0
+    current = @head
+    if current
+      while index < n


What if there are less than n+1 number of nodes in the list?
To fix for that scenario, Reverse the order of if and while statements and if current become null sooner than the n, return null.

shrutivanw · 2017-10-31T21:54:22Z

linked_list.rb

-        current = current.next
+    prevVal = nil
+    # nextVal = nil
+      until value < current.data


check if current is nil (or @Head is nil) before accessing current.data

shrutivanw · 2017-10-31T21:59:44Z

linked_list.rb

+
+    new_node = Node.new(value)
+
+    if value > current.data && !current.next


Check if current is nil first. :-)

Scenarios to ensure your code works for: empty linked list, linked list has all values smaller than the value to insert, linked list with all values greater than the value to insert. In the empty linked list case and all values greater than value to insert case, head will need to get updated.

shrutivanw · 2017-10-31T22:04:53Z

linked_list.rb

+    end
+    while current.data != value
+      prevNode = current
+      current.next ? current = current.next : break


Should this be current.next ? current = current.next : return If you just break, you'll have a nil dereference exception on line 142.

shrutivanw · 2017-10-31T22:07:22Z

linked_list.rb

+        prevNode.next = current.next
+      else
+        prevNode.next = nil
+      end


Optimization: you could replace lines 143 through 147 with just line 144, i.e. prevNode.next = current.next. If current.next is nil, line 144 will just set prevNode.next to nil.

shrutivanw · 2017-10-31T22:07:37Z

linked_list.rb

  end

  # method to reverse the singly linked list
  # note: the nodes should be moved and not just the values in the nodes
  def reverse
-    puts "Not implemented"
+    puts "THIS MAKES MY HEAD HURT"


shrutivanw · 2017-10-31T22:07:59Z

linked_list.rb

+    puts "THIS MAKES MY HEAD HURT"
+    current = @head
+    previous = nil
+    temp = current.next


Check for empty linked list case. Don't access current.next without verifying that current exists (and is not nil).

shrutivanw · 2017-10-31T22:15:26Z

Hi Aurora, see comments inline.

The common themes to watch out while working with linked lists are:

(i) always check and make sure that the node is not nil before accessing member variables (data, next or previous)

(ii) check if your method will work if

the linked list is empty (aka head is nil),
the linked list has less number of nodes than what you expect,
the linked list nodes have values that are all greater than a certain value,
the linked list nodes have values that are all less than a certain value,

(ii) and in the case of doubly linked list, don't forget to update previous along with next.

auroralemieux added 3 commits September 5, 2017 06:30

insert, search, visit, find_nth_from_beginning complete

ce09eb0

added max, min, length, insert ascending

3fdf30f

added find middle value, reverse

ee839f9

shrutivanw reviewed Oct 31, 2017

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Aurora Anderson Linked List #17

Aurora Anderson Linked List #17

auroralemieux commented Sep 6, 2017

shrutivanw Oct 31, 2017

shrutivanw Oct 31, 2017

shrutivanw Oct 31, 2017

shrutivanw Oct 31, 2017

shrutivanw Oct 31, 2017

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shrutivanw Oct 31, 2017

shrutivanw Oct 31, 2017 •

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shrutivanw commented Oct 31, 2017


		new_node = Node.new(value)

		if value > current.data && !current.next

Aurora Anderson Linked List #17

Are you sure you want to change the base?

Aurora Anderson Linked List #17

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auroralemieux commented Sep 6, 2017

Linked Lists

Comprehension Questions

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shrutivanw commented Oct 31, 2017

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