Made Easy test series

Question

Consider a stack implementation supports, in addition to PUSH and POP, an operation REVERSE, which reverses the order of the elements on the stack. Which of the following represents the minimum stack operations required to implement ENQUEUE and DEQUEUE operations of queue data structure respectively?

a) 1 and 3

b) 3 and 1

c) 2 and 2

d) Either a or b

Answer 1

Answer is either a or b therefore option D is right answer

let already in queue, there are a,b,c,d

inserting e 

How option A is right ?

For enqueue, ====>  push --------------> a,b,c,d,e

For dequeue, ====>  reverse, pop, reverse ------> i) e,d,c,b,a, ii) pop a, then stack look like e,d,c,b iii) b,c,d,e

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How option B is right ?

For enqueue, reverse,push,reverse

For dequeue, pop

 

for analyzing this , take empty queue, add a,b,c,d one by one, delete, add e and delete ===> queue now look like as c,d,e where c is front and e is rear

note that my representation, stack contains 1,2,3,4 means 1 is at bottom of the stack and 4 is at top of the stack

enqueue a :- 1) reverse  2) push a ( a )  3) reverse ( a ) ===> after enqueuing stack look like as  a

enqueue b :- 1) reverse ( a )  2) push b ( a,b )  3) reverse ( b,a ) ===> after enqueuing stack look like as  b,a

enqueue c :- 1) reverse ( a,b ) 2) push c ( a,b,c )  3) reverse ( c,b,a ) ===> after enqueuing stack look like as  c,b,a

enqueue d :- 1) reverse ( a,b,c )  2) push d ( a,b,c,d )  3) reverse ( d,c,b,a ) ===> after enqueuing stack look like as  d,c,b,a

dequeue :- 1) pop ===> after dequeuing stack look like as  d,c,b

enqueue e :- 1) reverse ( b,c,d )  2) push e ( b,c,d,e )  3) reverse ( e,d,c,b ) ===> after enqueuing stack look like as  e,d,c,b

dequeue :- 1) pop ===> after dequeuing stack look like as  e,d,c

Comments

You took a queue in support of option B.

i didn't take any queue...

 

 for analyzing this , take empty queue, add a,b,c,d one by one, delete, add e and delete ===> queue now look like as c,d,e where c is front and e is rear

 

i mean, what happen if you have queue.

 

By Stack implementation, i achieve the result as queue.

 

analyse one more time, my apporach...

You took a special case but answer should be general.

it is in terms of general only not a special case...

 

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

Repeated from previous year. Either of a or b true.

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Sorry Bro i didn't see it.... Finally Are you understand or not that matters