问题
Possible Duplicate:
Linked list recursive reverse
I searched my question on SO and got a link
recursion stack trace
I din't understand How the head_ref is Pointing to 4 there?
Could anyone help me to understand this?
回答1:
ok, first of all, it's 6 am here, and i couldn't sleep all night ... so this might be bullshit ;) ... but here we go:
the "magic" happens at recursiveReverse(&rest); ... the & says that the parameter is the address of rest ... since rest itself is a pointer, our param is a pointer to a pointer ...
when the function has finished, the pointer has been changed, and points to the first element of the reversed sub-list (which is the 4-Node) ...
EX:
so let's say we have our list 1 -> 2 -> 3 -> 4 and have called recursiveReverse(struct node** head_ref) with a pointer to a pointer to the 1-node as the head_ref parameter
so let's say head_ref is at a certain address (which i call A)
head_ref is a pointer to a pointer ... so the value at the address A is another address (let's call that B)
so the "thing" that is stored at B is a pointer ... so the value at B is also an address (let's call that address C)
finally the "thing" stored at C is our struct ...
now with this in mind, we make our first recursive call to recursiveReverse(struct node** head_ref) ... this time our parameter is &rest ... &rest is a pointer to a pointer to the 2-node...
let's have a closer look ... the value of &rest is an address ... (hard to guess, we call that D) ... the value at D is an address (the address of the 2-node) which we call E
after the recursive call has finished, the sub-list 2 -> 3 -> 4 has been reversed (4 -> 3 -> 2), and one of our addresses has been updated with a new value ... D has been updated, and no longer holds the address E, but the address of the 4-node (call that F if you want ...)
so now, we have the pointer "first" pointing to the 1-node which has its next-pointer still pointing at the 2-node... so with first->next->next = first, we correct the 2-nodes "next" pointer, to point at the 1-node ...
since the 1-node shall no longer point to the 2-node, we have first->next=NULL and now the complete list has been reversed ...
since we have no return value, we return our reversed list by the pointer to pointer parameter head_ref ... with *head_ref = rest
rest is a pointer ... it's located at address D ... the current value at D is F (address of the 4-node)
so we write the value of D (which is F, the address of the 4-node) to the Address B (which is *head_ref)
and that is how the pointer to the 4-node is returned
来源：https://stackoverflow.com/questions/12408178/confusion-in-reversing-a-linked-list-through-recursion