Stacks GATE CS PYQ Quiz

Assume that the operators +, -, × are left associative and ^ is right associative. The order of precedence (from highest to lowest) is ^, x , +, -. The postfix expression corresponding to the infix expression a + b × c - d ^ e ^ f is

The result evaluating the postfix expression 10 5 + 60 6 / * 8 – is

Consider the following sequence of operations on an empty stack.

Push(54);push(52);pop();push(55);push(62);s=pop(); 

Consider the following sequence of operations on an empty queue.

enqueue(21);enqueue(24);dequeue();enqueue(28);enqueue(32);q=dequeue(); 

The value of s+q is ___________.

An implementation of a queue Q, using two stacks S1 and S2, is given below:

void insert(Q, x) {
   push (S1, x);
}
 
void delete(Q){
   if(stack-empty(S2)) then 
      if(stack-empty(S1)) then {
          print(“Q is empty”);
          return;
      }
      else while (!(stack-empty(S1))){
          x=pop(S1);
          push(S2,x);
      }
   x=pop(S2);
}

Let n insert and m (<=n) delete operations be performed in an arbitrary order on an empty queue Q. Let x and y be the number of push and pop operations performed respectively in the process. Which one of the following is true for all m and n?

A single array A[1..MAXSIZE] is used to implement two stacks. The two stacks grow from opposite ends of the array. Variables top1 and top2 (topl< top 2) point to the location of the topmost element in each of the stacks. If the space is to be used efficiently, the condition for “stack full” is

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

Let S be a stack of size n ≥ 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 one such stack operation and the start of the next operation. For m ≥ 1, define the stack-life of m as the time elapsed from the end of 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

What is the minimum number of stacks of size n required to implement a queue of size n?

Let Q denote a queue containing sixteen numbers and S be an empty stack. Head(Q) returns the element at the head of the queue Q without removing it from Q. Similarly Top(S) returns the element at the top of S without removing it from S. Consider the algorithm given below.

while Q is not Empty do 
  if S is Empty OR Top(S) ≤ Head (Q) then 
     x:= Dequeue (Q); 
     Push (S, x); 
  else  
     x:= Pop(S); 
     Enqueue (Q, x);
  end
 end

The maximum possible number of iterations of the while loop in the algorithm is______ [This Question was originally a Fill-in-the-Blanks 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?