Implement a stack using queue

This updated information has been further expanded upon on my new website. You can find the updated details here: https://k5kc.com/cs/algorithms/implement-stack-using-queues/.

Problem - Implement a stack using a queue

Solution

Method 1 - Implement a stack using 2 queues
We have already discussed the problems here.

Method 2 - Implement a stack using a single queue
Here are the operations(note that push operation is expensive)

push:

1. enqueue new element.
2. If n is the number of elements in the queue, then remove and insert element n-1 times.

pop:

1. dequeue

push 1


front                     
+----+----+----+----+----+----+
| 1  |    |    |    |    |    |    insert 1
+----+----+----+----+----+----+


push2

front                     
+----+----+----+----+----+----+
| 1  | 2  |    |    |    |    |    insert 2
+----+----+----+----+----+----+

     front                     
+----+----+----+----+----+----+
|    | 2  |  1 |    |    |    |    remove and insert 1
+----+----+----+----+----+----+




 insert 3


      front                     
+----+----+----+----+----+----+
|    | 2  |  1 |  3 |    |    |    insert 3
+----+----+----+----+----+----+

           front                     
+----+----+----+----+----+----+
|    |    |  1 |  3 |  2 |    |    remove and insert 2
+----+----+----+----+----+----+

                front                     
+----+----+----+----+----+----+
|    |    |    |  3 |  2 |  1 |    remove and insert 1
+----+----+----+----+----+----+

Code:

int stack_pop (queue_data *q)
{
  return queue_remove (q);
}

void stack_push (queue_data *q, int val)
{
  int old_count = queue_get_element_count (q), i;

  queue_insert (q, val);
  for (i=0; i<old_count; i++)
  {
    queue_insert (q, queue_remove (q));
  }
}

Thanks.