Similar --> https://gateoverflow.in/2007/gate2014-2-41

Suppose a stack implementation supports, in addition to PUSH and POP, an operation REVERSE, which reverses the order of the elements on the stack.

- To implement a queue using the above stack implementation, show how to implement ENQUEUE using a single operation and DEQUEUE using a sequence of $3$ operations.
- The following post fix expression, containing single digit operands and arithmetic operators $+$ and $*$, is evaluated using a stack.

$5 \ 2 * 3 \ 4 + 5 \ 2 * * +$

Show the contents of the stack- After evaluating $5 \ 2 * 3 \ 4 +$
- After evaluating $5 \ 2 * 3 \ 4 + 5 \ 2$
- At the end of evaluation

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## 2 Answers

### 5 Comments

@Mizuki....can you explain with this example..please

For dequeue operation do the following

**-reverse, pop, reverse **

@ VIDYADHAR SHELKE 1 Consider that the stack initially contains the elements 1,2,3,4 from bottom to top (i.e 4 is at the top)

Consider 2 operations to be performed

1) Dequeue

2) Enqueue(5)

For 1)

We'll have to first reverse the stack. So stack contents 4,3,2,1 from bottom to top.

Next,we'll pop the element. So stack contents 4,3,2.

Now we'll have to reverse the elements,since we want to enqueue in 1 operation(if we dont reverse then 5 will be pushed after 2,but it should be pushed after 4). So stack contents 2,3,4.

Now Enqueue(5) . So stack contents 2,3,4,5 from bottom to top.

Hence, total Dequeue operations =3 and Enqueue operations = 1.