134. OCR A Level (H446) SLR23 – 2.2 Recursion

What is recursion?

• A function calling another function

• A method to increase memory usage

• A function calling itself

• A loop that executes indefinitely

Answer explanation

Recursion is a process where a function calls itself, allowing tasks to be solved by breaking them down into smaller instances of the same task.

What should a recursive subroutine contain?

• An infinite loop

• A stopping condition

• A global variable

• A for loop

Answer explanation

A recursive subroutine should contain a stopping condition to prevent infinite recursion and ensure the function terminates correctly.

What happens without a stopping condition in a recursive subroutine?

• It may call itself indefinitely

• It executes faster

• It uses less memory

• It becomes an iterative subroutine

Answer explanation

Without a stopping condition, a recursive subroutine may call itself indefinitely, leading to infinite recursion and potential stack overflow.

What is the factorial of 3?

• 12

• 3

• 9

• 6

Answer explanation

The factorial of 3 is calculated as 3 x 2 x 1 = 6. Therefore, the correct answer is 6.

Which approach did the video suggest is more memory efficient for calculating factorials?

• Iteration

• Both are equally efficient

• Recursion

• Neither, it depends on the programming language

Answer explanation

The video suggested that the Iteration approach is more memory efficient for calculating factorials compared to Recursion.

What can cause a stack overflow?

• Using an iterative approach

• Using a for loop

• Declaring too many variables

• A recursive subroutine calling itself too many times

Answer explanation

A stack overflow can be caused by a recursive subroutine calling itself too many times, leading to the stack memory being exhausted.

What is the result of 4 factorial?

• 16

• 12

• 8

• 24

Answer explanation

The result of 4 factorial is calculated as 4 x 3 x 2 x 1 = 24. Therefore, the correct answer is 24.

What does the processor need to remember for each recursive call?

• The number of times the function has been called

• Where it was before the jump and the values of all previous variables

• The location of the next instruction

• The value of global variables

Answer explanation

The processor needs to remember where it was before the jump and the values of all previous variables for each recursive call.

What is a base case in recursion?

• A stopping condition

• A special case for optimization

• The first call of the recursion

• The final call of the recursion

Answer explanation

A base case in recursion is a stopping condition that prevents the function from calling itself infinitely, allowing the recursion to reach a conclusion.

Why is recursion not always the best approach?

• It cannot solve complex problems

• It is always the best approach

• It is slower than iteration in all cases

• It uses more memory due to the call stack

Answer explanation

Recursion is not always the best approach because it uses more memory due to the call stack, which can lead to stack overflow errors when dealing with large datasets or deep levels of recursion.