GATE CS 2014 Set 2 — Question 51
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Programming & Data Structures → Stacks & Queues → Queue & Circular Queue
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Question
Suppose a stack implementation supports an instruction REVERSE, which reverses the order of elements on the stack, in addition to the PUSH and POP instructions. Which one of the following statements is TRUE with respect to this modified stack?
Correct answer
(C) A queue can be implemented where ENQUEUE takes a sequence of three instructions and DEQUEUE takes a single instruction.
Solution
A queue (FIFO) can be implemented using a stack (LIFO) with the REVERSE operation as follows:To maintain the queue order such that the front of the queue is always at the top of the stack (allowing Dequeue):ENQUEUE(x):
1.REVERSE (Reverses stack so the rear is at the top)
2.PUSH(x) (Adds new element to the rear)
3.REVERSE (Reverses stack back so the front is at the top)
Total: 3 instructions.DEQUEUE():1.POP (Removes the front element from the top)
Total: 1 instruction.Thus, option (C) is correct.Continue learning with Success Tracker
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