GATE PYQ

Stack

Q21.
The infix expression A+(B-C)^*D is correctly represented in prefix notation as

Q22.
The five items: A, B, C, D, and E are pushed in a stack, one after other starting from A. The stack is popped four items and each element is inserted in a queue. The two elements are deleted from the queue and pushed back on the stack. Now one item is popped from the stack. The popped item is

Q23.
The best data structure to check whether an arithmetic expression has balanced parenthesis is a:

Q24.
Which of the following permutations can be obtained in the output (in the same order) using a stack assuming that the input is the sequence 1, 2, 3, 4, 5 in that order?

Q25.
The best data structure to check whether an arithmetic expression has balanced parentheses is a

Q26.
Stack A has the entries a, b, c (with a on top). Stack B is empty. An entry popped out of stack A can be printed immediately or pushed to stack B. An entry popped out of the stack B can be only be printed. In this arrangement, which of the following permutations of a, b, c are not possible?

Q27.
To evaluate an expression without any embedded function calls

Q28.
A program attempts to generate as many permutations as possible of the string, 'abcd' by pushing the characters a,b,c,d in the same order onto a stack, but it may pop off the top character at any time. Which one of the following strings CANNOT be generated using this program?

Q29.
The five items: A, B, C, D, and E are pushed in a stack, one after other starting from A. The stack is popped four items and each element is inserted in a queue. The two elements are deleted from the queue and pushed back on the stack. Now one item is popped from the stack. The popped item is

Q30.
Let S be a stack of size n \geq 1. Starting with the empty stack, suppose we push the first n natural numbers in sequence, and then perform n pop operations. Assume that Push and Pop operation take X seconds each , and Y seconds elapse between the end of the one such stack operation and the start of the next operation. For m \geq 1, define the stack-life of m as the time elapsed from the end or Push (m) to the start of the pop operation that removes m from S . The average stack-life of an element of this stack is