Deleting a list element at the tail of a linked list
My problem:
Deleting a list element at the tail of a linked list
The solution of my problem is:
We need to find an (recursive) algorithm that solves My Problem.
Designing a recursive algorithm
to delete at tail
Consider the smaller problem delete(head->next):
Designing a recursive algorithm
to delete at tail
The solution of delete(head.next) is:
Designing a recursive algorithm
to delete at tail
Suppose we have the solution of delete(head.next) avialable:
How can we use this solution to solve our original problem ?
Designing a recursive algorithm
to delete at tail
Answer:
So: what is the (recursive) algorithm ?
Designing a recursive algorithm
to delete at tail
The recursive algorithm:
helpSol
=
delete( h->next ) ; --- ask
someone else to
solve this
smaller problem
Designing a recursive algorithm
to delete at tail
The recursive algorithm:
helpSol
=
delete( h->next ) ; --- ask
someone else to
solve this
smaller problem
head->next
=
helpSol ; ---
use the
smaller solution to
solve
my problem !
Base case #1 for delete at tail
Base case #1: delete in an empty list
Solution:
Algorithm:
return NULL;
Base case #2 for delete at tail
Base case #1: delete the last element from a list
Solution:
Algorithm:
free(head) ; --- we must
de-allocate the
deleted element
ourselves !
return NULL;
Recursive algorithm to
delete at tail of a linked list
struct List *delete( struct List *head, struct List *e )
{
struct List * helpSol;
/* --------------------------------------------
Base case: delete at the tail of an empty
-------------------------------------------- */
if ( head == NULL )
{
return(NULL); // Empty list
}
else if ( head->next == NULL )
{
free(head) ; // De-allocate deleted element
return(NULL); // Empty list
}
else
{
/* ===========================================================
Solve the problem USING the solution of a smaller problem
=========================================================== */
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DEMO: /home/cs255001/demo/C/Recursion/delete-tail.c
Simplified recursive algorithm to
delete at tail of a linked list
struct List *delete( struct List *head, struct List *e )
{
/* --------------------------------------------
Base case: delete at the tail of an empty
-------------------------------------------- */
if ( head == NULL )
{
return(NULL); // Empty list
}
else if ( head->next == NULL )
{
free(head) ; // De-allocate deleted element
return(NULL); // Empty list
}
else
{
/* ===========================================================
Solve the problem USING the solution of a smaller problem
=========================================================== */
head->next = delete( head->next ); // Link directly to helpSol
return head; // Return MY solution
}
}
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