Linked Lists 2
The Big O
As you arrive…
1. Snarf the code for today’s class
2. Grab a worksheet
3. Take a look at the constructor for the LinkedList class
you snarfed that takes an int[]. Try to understand
how to works. Feel free to run and play with the
code to understand it.
Take a look at the constructor for the LinkedList class you
snarfed that takes an int[]. Which of these statements
best describes its operation?
1. It goes through each element of the input array in
order, and adds them to the head of the linked list. As
a result, the list is the reverse of the array.
2. It goes through each element of the input array in
order, and adds them to the tail (end) of the linked
list. As a result, the list is the and the array are in the
same order.
3. It goes through each element of the input array in
reverse and adds them to the head of the linked list.
As a result, the list is the and the array are in the same
order.
4. It goes through each element of the input array in
reverse and adds them to the tail of the linked list. As
a result, the list is the reverse of the array.
On the agenda: More Practice With
Linked Lists
1.
2.
3.
4.
Getting Elements in Linked Lists
Removing Elements in Linked Lists
The DNA Assignment
Madness
Inner Class (Reprise)
Getting elements in a linked list
• Write a function getElement(int i) that takes
an index and returns the element in a linked
list at that index
• If the element is not in the list, return -1
• This has a very cute recursive solution, BTW
• If you finish that, write a function
getMiddleElement() that returns the middle
element of a linked list
Removing Elements from a Linked List
• Write a function removeFours that removes all the
elements with value 4
• You can assume that the first element in the linked list
will not be a four.
• I’ve got 2 hints at the bottom of the source file, if you
get stuck
• If you finish, change your function so it works if the
first element is a 4 (there is a cool recursive formation,
but it’s a bit tricky to get)
• If you finish that, write a new version of your function
that is iterative (i.e. non-recursive) or if you did it
iteratively first, do it recursively
What do you suppose the Big-O of the
following Linked List Operations Are?
• Work with those nearby to fill out the
worksheet
Linked List Big O – Summing Up
• Linked Lists are good when you need to add or
remove a lot of elements
• Linked Lists are not so good when you have to
access a lot of specific indexes
• Sometimes for optimal behavior you have to
keep track of specific nodes rather than
iterating across the list multiple times
DNA
Linked Lists: Into the Mouth of
Madness
• Write a function mergeLists that takes two linked
lists as parameters. It should insert the second
list into the first list after the first “0” element in
the first list
• If there’s no 0 in the first list, both lists should be
unmodified
• If you finish, write the recursive version (you
might need 2 recursive functions for this one)
• If you finish, change your function so that rather
than modifying the existing list in returns a new
list which is the merge