Question

What is the entry returned by the peek() method after the following operations on a stack:
push(A), push(R), pop(), push(D),  pop(), push(L), pop(), push(J), push(S), pop(), pop()

Group of answer choices

A

S

L

D

J

Which of the following is true about the Stack interface we implemented in class?

Group of answer choices

You can only pop from the top of the stack but you can peek at any entry on the stack

The bottom item in a stack is the last item added

The first item added to a stack is the first one removed

To access the item at the bottom of the stack we have to pop() all items on top of it

None of the above is true

The postfix expression corresponding to a + (c - d) / (b * r) is

Group of answer choices

a c d - b r * / +

a c d - + b r * /

a + c d - / b r *

a c + d * b r - /

none of the above

The postfix expression a b * c + d - is equivalent to the following infix expression

Group of answer choices

d - c + b * a

d - (c + b * a)

a * ( b + c - d)

a * b + c - d

None of the above

Answer 1

Question 1:

What is the entry returned by the peek() method after the following operations on a stack:
push(A), push(R), pop(), push(D),  pop(), push(L), pop(), push(J), push(S), pop(), pop()

Answer 1:

Stack abstract data type follows last in first out approach to process data.

The sequece of elements in the stack after each operations:

push(A)

Stack: A

push(R)

Stack: R A

pop()

Stack: A

push(D)

Stack: D A

pop()

Stack: A

push(L)

Stack: L A

pop()

Stack: A

push(J)

Stack: J A

push(S)

Stack: S J A

pop()

Stack: J A

pop()

Stack: A

Now on peek(), A will be returned.

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Question 2:

Which of the following is true about the Stack interface we implemented in class?

You can only pop from the top of the stack but you can peek at any entry on the stack

The bottom item in a stack is the last item added

The first item added to a stack is the first one removed

To access the item at the bottom of the stack we have to pop() all items on top of it

None of the above is true

Answer 2:

True options is:

To access the item at the bottom of the stack we have to pop() all items on top of it

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Question 3:

The postfix expression corresponding to a + (c - d) / (b * r)

Answer 3:

Sequence No.	Input Expression	Stack	Postfix Expression
1	a		a
2	+	+	a
3	(	+(	a
4	c	+(	ac
5	-	+(-	ac
6	d	+(-	acd
7	)	+	acd-
8	/	+/	acd-
9	(	+/(	acd-
10	b	+/(	acd-b
11	*	+/(*	acd-b
12	r	+/(*	acd-br
13	)	+/	acd-br*
14		+	acd-br*/
15			acd-br*/+

So, the postfix expression will be: a c d - b r * / +

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Question 4:

The postfix expression a b * c + d - is equivalent to the following infix expression

Answer 4:

Sequence No.	Input Expression	Stack	Infix Expression
1	a	a
2	b	ab
3	*	(a*b)	(a*b)
4	c	(a*b)c	(a*b)
5	+	((a*b)+c)	((a*b)+c)
6	d	((a*b)+c)d	((a*b)+c)
7	-	((a*b)+c) - d	((a*b)+c) - d

So, the infix expression is a * b + c - d

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