- Another popular way to insert elements into a linked list is
ordered by the value that is inserted.
- These notes show you have you what you must do to maintain the elements in a linked list in ascending order... However, I do not provide any program code. You have to figure out the details using what you have learned in a homework project.
- Pictorial representation of the BEFORE and AFTER states:
- Algorithm: Ordered List
- Use
TWO pointer variables
pointing to
adjacent list elements :
- p1 initially points to the first element
- p2 initially points to the second element
- Find adjacent elements
p1 and
p2 in the list such that:
- p1->value is smaller than or equal to the new element
- p2->value is greater than or equal to the value in the new element
- Link new element between
p1
and
p2
- Make p1->next point to the new element (the new element will thus "follow" this element)
- Set the "next" linkage variable in the new element to point to p2 (the element p2 follows the new element)
Pictorial representation of the insert algorithm:
- Use
TWO pointer variables
pointing to
adjacent list elements :
- There are 2 exception cases
that must be handled
differently when inserting
in an ordered list:
- When the list is
empty
- When the new element that is inserted as first element of the list
All other cases can be handle by the insertion algorithm described above.
- When the list is
empty
- Special case 1:
inserting in
an EMPTY list:
- How to detect this case:
if ( head == NULL ) { .... } - How to handle insertion in this special case:
Handle it in the same way as in the "insert at tail" example....
- How to detect this case:
- Special case 2:
new element inserted at
start of
an non-empty list:
- How to detect this case:
if ( newElem->value <= head->value ) { .... } - How to handle insertion in this special case:
Handle it in the same way we have handle insertion at the head of a list.
- How to detect this case:
- Algorithm skeleton:
if ( head == NULL ) { code to handle insert for special case 1 } else if ( newElem->value <= head->value ) { code to handle insert for special case 2 } else { code to handle insert for all other cases }