Question

I’m trying to illustrate a doubly linked list problem. this is from an old test i’ve been studying lately.

The question is as follows:

draw what the final linked after this code:

ListNode n1 = new ListNode();
ListNode n2 = new ListNode();
ListNode n3 = n1;
n1.next = n2;
n3.prev = n1;
n1.next.prev = n3.next;

Where I get lost is the final line of code.

n1.next.prev = n3.next;

here’s the solution:

http://www.imagechicken.com/viewpic.php?p=1242322384048558300&x=jpg

can anyone walk me through this one or lead me in a good direction?

Answer 1

The key to this one is that n1 and n3 point to the same ListNode.

Here are the states after each of the 3 operations:

n1.next = n2;
// n1.prev = null;
// n1.next = n2;
// n2.prev = null;
// n2.next = null;
// n3.prev = null;
// n3.next = n2;

n3.prev = n1;
// n1.prev = n1;
// n1.next = n2;
// n2.prev = null;
// n2.next = null;
// n3.prev = n1;
// n3.next = n2;

n1.next.prev = n3.next;
// n1.prev = n1;
// n1.next = n2;
// n2.prev = n2;
// n2.next = null;
// n3.prev = n1;
// n3.next = n2;

So in that last statement, n3.next is the same as n1.next, which is n2. Thus, the last statement is equivalent to settings n2.prev = n2.