Deck 7: Stacks

Question 1

The time complexity of the postfix expression evaluation algorithm is O( n² ) .

Answer 1

not answer

Question 2

When converting from infix form to postfix form, parentheses are added to the equation.

Answer 2

False

Question 3

With a stack, you always access the item that has been most recently added.

Answer 3

True

Question 4

When using a stack to determine if brackets are balanced in an expression, the stack should not be empty when you reach the end of the expression.

Question 5

Access to a stack is restricted to the bottom end.

Question 6

The first step in evaluating a postfix expression is to scan the expression from left to right.

Question 7

The push operation for a stack raises an error if the stack is empty.

Question 8

The operator in an infix expression follows the operands.

Question 9

Stacks adhere to a LIFO protocol.

Question 10

Stack interfaces implement a peek operation for examining the element at the top of the stack.

Question 11

The pop operation for a stack raises an error if the stack is empty.

Question 12

The operator in a postfix expression follows the operands.

Question 13

The equation 17 46 + is an example of postfix form.

Question 14

When evaluating an arithmetic expression, first you transform it from its postfix form to its infix form.

Question 15

A stack structure is a built-in part of the Python language.

Question 16

A token in the postfix expression evaluation algorithm is an operand or operator.

Question 17

The operation for removing an item from the stack is called push.

Question 18

A Python list structure and its methods implement a stack perfectly.

Question 19

A tuple is an immutable collection type.

Question 20

Using a stack is a good approach to determining if the use of brackets in an expression is balanced.

Question 21

In a linked structure stack implementation, efficient pushing and popping require adding and removing of nodes at the head of the linked sequence.

Question 22

What protocol are stacks said to adhere to?

A) LIFO
B) FIFO
C) one-to-one
D) many-to-one

Question 23

To avoid stack overflow, the stack algorithm should raise an error if an item is added to a full stack.

Question 24

What is the operation that adds items to a stack?

A) get
B) set
C) push
D) pop

Question 25

Which of the following is true about stacks?

A) they are analogous to a row of books on a shelf
B) items are always added to the bottom
C) access is restricted to just one end
D) most implementations allow access to the middle

Question 26

Because of their linear structure, stacks can only be implemented using linked structures.

Question 27

When using a stack to evaluate the balance of brackets and parentheses in an expression, what is the first step?

A) push opening brackets onto the stack while scanning the expression
B) pop closing brackets onto the stack while scanning the expression
C) push closing brackets onto the stack while scanning the expression
D) pop opening brackets onto the stack while scanning the expression

Question 28

Which of the following is true about a postfix expression?

A) the operator is between its two operands
B) the operator follows its two operands
C) stack of bricks
D) table of contents

Question 29

Which of the following is NOT an application of stacks in computer science?

A) implementation of a hash-based database search function
B) managing computer memory in support of function calls
C) supporting the undo feature in a text editor
D) maintaining a history of visited links by a web browser

Question 30

What is the first step in the algorithm to evaluate an arithmetic expression?

A) transform the expression from postfix form to infix form
B) calculate the result from the postfix expression
C) calculate the result from the infix expression
D) transform the expression from infix form to postfix form

Question 31

The Node class for use in the linked structure stack contains three fields: data, next, and previous.

Question 32

In the algorithm that checks for a balanced expression, which of the following is true if a closing bracket is encountered?

A) if the stack is empty, the brackets balance
B) if the item on the top of the stack is a closing bracket of the same type, the brackets balance
C) if the stack is empty or the item on the top of the stack is not an opening bracket of the same type, the brackets don't balance
D) if the stack is empty or the item on the bottom of the stack is an opening bracket of the same type, the brackets balance

Question 33

When using a stack to evaluate the balance of brackets and parentheses in an expression, what is the final step?

A) at the end of the expression, if a final closing bracket is found, the brackets balance
B) at the end of the expression, if the stack is empty, the brackets do not balance
C) at the end of the expression, if the stack is full, the brackets balance
D) at the end of the expression, if the stack is empty, the brackets balance

Question 34

In the algorithm to evaluate a postfix expression, what does the algorithm do when an operator is encountered?

A) pop the resulting value from the stack
B) push the preceding operands onto the stack
C) apply the operator to the two preceding operands
D) push the operator onto the stack

Question 35

Which of the following is NOT an example of a stack in everyday life?

A) a spindle of blank DVDs
B) a stack of plates in a cafeteria line
C) a pile of napkins
D) a jar of jellybeans

Question 36

Addition and subtraction have higher precedence when evaluating an infix expression.

Question 37

If the current state of the stack is [ x, y, z ] where x is the bottom of the stack and z is the top of the stack, what is the state of the stack and the value returned after a pop operation?

A) the state is [ x, y ]; z is returned
B) the state is [ x, y, z ]; z is returned
C) the state is [ y, z ]; x is returned
D) the state is [ x, y, z ]; x is returned

Question 38

What is the function of the peek method in a stack implementation?

A) to return the bottom item without removing it
B) to return the top item without removing it
C) to return the top item and remove it from the stack
D) to return the bottom item and remove it from the stack

Question 39

Which of the following is NOT an operation supported by a stack interface?

A) push
B) insert
C) clear
D) peek

Question 40

In what way doesn't the Python list data structure accurately emulate a stack?

A) the append method pushes elements onto the stack
B) the pop method removes and returns the top element
C) a list uses an array as the underlying data structure
D) list methods allow manipulation of items at any position

Question 41

Which of the following begins in a predefined starting state and then moves from state to state in search of a desired ending state?

A) backtracking algorithm
B) memory management algorithm
C) infix to postfix converter
D) postfix to infix converter

Question 42

In the linked implementation of a stack, what type of helper function simplifies the __iter__ method?

A) binary
B) sequential
C) recursive
D) random

Question 43

If the portion of the postfix expression scanned so far is 7 6 2 +, what is the result when the operator is applied to the operands?

A) 8
B) 15
C) 13
D) 9

Question 44

In the following code that defines the push method for the array-based stack, what is the missing code? def push (self, item):
< missing code >
Self.size += 1

A) self.items += 1
B) self.items[ len(self) ] = item
C) items[ size ] = len(self.item)
D) item = self.items[ self.size + 1 ]

Question 45

In the algorithm to evaluate a postfix expression, what does the algorithm do when an operand is encountered?

A) pop the operand from the stack
B) push the operand onto the stack
C) pop the operator from the stack
D) push an operator onto the stack

Question 46

What is the resulting infix expression from the following postfix expression? 17 4 - 6 + 8 *

A) 17 - (4 + 6 * 8)
B) 17 - (4 + 6) * 8
C) (17 - 4) + (6 * 8)
D) (17 - 4 + 6) * 8

Question 47

If the entire postfix expression is 9 1 4 + - 2 *, what is the final value?

A) 12
B) 8
C) 17
D) 10

Question 48

What is the function of the PVM?

A) converts methods to subroutines
B) executes a python program from bytecodes
C) compiles Python code into assembly language
D) links a Python program to imported modules

Question 49

What is the resulting postfix expression from the following infix expression? (12 + 5) * 2 - 3

A) 12 5 2 + * 3 -
B) 12 5 + 2 3 * -
C) 12 5 + 2 * 3 -
D) 12 5 2 + 3 - *

Question 50

What are the two fields required by the Node class in the linked implementation of a stack?

A) prev, items
B) prev, data
C) items, next
D) data, next