Inserting a list element at the tail of a linked list
My problem:
Inserting a list element at the tail of a linked list
The solution of my problem is:
Designing a recursive algorithm
to insert at tail
Consider the smaller problem insert(head.next, e):
Designing a recursive algorithm
to insert at tail
The solution of insert(head.next, e) is:
Designing a recursive algorithm
to insert at tail
Suppose we have the solution of insert(head.next, e) avialable:
How can we use this solution to solve our original problem ?
Designing a recursive algorithm
to insert at tail
Answer:
What remains: find a simple case to use a base case
Base case for insert at tail
Base case: (insert in an empty list)
Solution:
Recursive algorithm to
insert at tail of a linked list
public static List insert( List head, List e )
{
List helpSol;
/* --------------------------------------------
Base case: insert at the tail of an empty
-------------------------------------------- */
if ( head == null )
{
|
DEMO: /home/cs255001/demo/recursion/InsertList.java
Simplified recursive algorithm to
insert at tail of a linked list
public static List insert( List head, List e )
{
/* --------------------------------------------
Base case: insert at the tail of an empty
-------------------------------------------- */
if ( head == null )
{
e.next = null; // Mark e as the last list elem
return(e); // e is the first list elem !
}
else
{
/* ===========================================================
Solve the problem USING the solution of a smaller problem
=========================================================== */
head.next = insert( head.next, e ); // Link directly to helpSol
return head; // Return MY solution
}
}
|
Recursive insert algorithm in ARM assembler
The Insert(head, p) function in ARM assembler:
Insert:
/* =============================
Prelude: build stack frame
============================= */
push {lr}
push {fp}
mov fp, sp
sub sp, sp, #0 // No local variables
// if ( h == null )
ldr r0, [fp, #8] // r0 = h
cmp r0, #0
bne else
// e.next = null
mov r0, #0 // r0 = null
ldr r1, [fp, #12] // r1 = e
str r0, [r1, #4] // e.next = null
// return e
ldr r0, [fp, #12] // r0 = e (return value)
b postLude
else:
// h.next = Insert( h.next, e );
//// pass e
ldr r0, [fp, #12] // r0 = e
push {r0} // Pass e with stack
//// pass h.next
ldr r0, [fp, #8] // r0 = h
ldr r0, [r0, #4] // r0 = h.next
push {r0} // Pass h.next with stack
bl Insert
add sp, sp, #8 // Clean up 2 parameters
//// Assign return value (in r0) to h.next
ldr r1, [fp, #8] // r1 = h - can't use r0!!
str r0, [r1, #4] // h.next = Insert(h.next,e)
// return( h );
ldr r0, [fp, #8] // r0 = h (return value)
postLude:
// Postlude - clean up and return to caller
mov sp, fp
pop {fp}
pop {pc}
|
DEMO: /home/cs255001/demo/asm/9-list-recursion/ARM-Insert.s