Review Linked List Insertion Description Deletion Description Basic Node Implementation Conclusion 1

Linked List Traversal Inserting into a linked list involves two steps: Find the correct location Do the work to insert the new value We can insert into any position Front End Somewhere in the middle (to preserve order) 2

Linked List Traversal Traversal means “visiting” or examining each node. Simple linked list Start at the beginning Go one node at a time until the end Recursive procedure (or function) Given a head pointer Looks at just one node What procedure will look at the rest? 3

The Node Code Node definesa record data isoftype Num next isoftype Ptr toa Node endrecord 4

The Big Picture 42 heap stack head LB 5

The Little Picture 12 6

The Classic Code Procedure Traverse (current isoftype in Ptr toa Node) // Precon: Pass in pointer to a list // Purpose: Print each data item // Postcon: No changes to list if(current <> NIL) then print(current^.data) Traverse(current^.next) endif endprocedure // Traverse 7

The Big Picture 42 heap stack head

9 Insertion Into Linked Lists

Node Definition node definesa record data isoftype Num next isoftype ptr toa node endrecord 10

The Scenario You have a linked list Perhaps empty, perhaps not Perhaps ordered, perhaps not You want to add an element into the linked list head // 11

Adding an Element to a Linked List Involves two steps: Finding the correct location Doing the work to add the node 12

Finding the Correct Location Three possible positions: The front The end Somewhere in the middle 13

head Inserting to the Front There is no work to find the correct location Empty or not, head will point to the right location head 93 14

Inserting to the End Find the end of the list (when at NIL) Recursion or iteration head // 93 // Don’t Worry! 15

Inserting to the Middle Used when order is important Go to the node that should follow the one to add Recursion or iteration head // 93 //

The Work to Add the Node Create the new node Fill in the data field Deal with the next field Point to nil (if inserting to end) Point to current (front or middle) temp <- new(Node) temp^.data <- new_data temp^.next <- current current <- temp 17

Three Types of Insertion To front No recursion needed To end Get to the end, then add node In order (in middle) To maintain sorted property 18

19 Inserting at the Front of a Linked List

Inserting to the Front of a Linked List Need an in/out pointer parameter Create new node Fill in data Make new node’s next pointer point to current Update current to point to new node 20

procedure Insert (current iot in/out ptr toa Node, new_data isoftype in Num) temp isoftype ptr toa Node temp <- new(Node) temp^.data <- new_data temp^.next <- current current <- temp endprocedure 4 17 head 42 Current new_data temp 2 R 2 Animated Insert to Front of Linked List (current iot in/out ptr toa Node, temp <- new(Node) temp^.data <- new_data temp^.next <- current current <- temp 21

22 Inserting at the End of a Linked List

Inserting to End of a Linked List Recursively traverse the list until at end Then: Create new node at current Fill in data Terminate the new node’s next pointer to point to NIL 23

Inserting to the End of a Linked List procedure Add_To_End( current isoftype in/out Ptr toa Node, new_data isoftype in Num ) // Purpose: Add new node to end of list // Pre: current points to NIL-terminated list // Post: new list has added element at end if( current = NIL ) then current <- new( Node ) current^.data <- new_data current^.next <- NIL else Add_To_End( current^.next, new_data) endif endprocedure //Add_To_End 24

head 53 current new_data 53 R R R R Inserting at the End of a Linked List 25

Inserting in Order into a Linked List

Inserting In Order into a Linked List Recursively traverse until you find the correct place to insert Compare to see if you need to insert before current If adding largest value, then insert at the end Perform the commands to do the insertion Create new node Add data Update the next pointer of the new node Update current to point to new node 27

Inserting in Order into a Linked List procedure Insert_In_Order(current isoftype in/out Ptr toa Node, new_data isoftype in Num ) // comments here temp isoftype Ptr toa Node if ((current = NIL) OR (current^.data > new_data)) then temp <- new( Node ) temp^.data <- new_data temp^.next <- current current <- temp else Insert_In_Order(current^.next,new_data) endif endprocedure //Insert_In_Order 28

Head Inserting In Order into a Linked List 19 current new_data temp R 19 current new_data temp R 19 current new_data temp R 19 29

Summary Inserting into a linked list involves two steps: Find the correct location Do the work to insert the new value We can insert into any position Front End Somewhere in the middle 30