Factorial Using Recursion in DSA Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is recursion in programming?

Recursion is when a function calls itself to solve smaller parts of a problem until it reaches a simple case it can solve directly.

beginner

What is the factorial of a number?

The factorial of a number n (written as n!) is the product of all positive integers from 1 up to n. For example, 4! = 4 × 3 × 2 × 1 = 24.

beginner

What is the base case in a recursive factorial function?

The base case is when n equals 0 or 1, and the factorial is 1. This stops the recursion from continuing forever.

intermediate

How does the recursive factorial function calculate factorial for n > 1?

It multiplies n by the factorial of (n - 1), calling itself with a smaller number until it reaches the base case.

beginner

Show the TypeScript function signature for a recursive factorial function.

function factorial(n: number): number

What is the factorial of 0?

A Undefined

B 0

C Cannot be calculated

D 1

By definition, 0! is 1 to serve as the base case in factorial calculations.

In recursion, what prevents infinite calls?

A Loop

B Base case

C Variable declaration

D Function parameters

The base case stops recursion by providing a simple answer without further calls.

What does factorial(4) compute in recursion?

A 4 × factorial(3)

B 4 + factorial(3)

C factorial(3) only

D 4 × 3

factorial(4) calls factorial(3) and multiplies the result by 4.

Which of these is a correct base case for factorial recursion?

A if (n > 1) return n * factorial(n - 1);

B if (n === 1) return 0;

C if (n === 0) return 1;

D if (n < 0) return 1;

The base case returns 1 when n is 0 to stop recursion.

What will happen if the base case is missing in a recursive factorial function?

A The function will call itself forever and cause an error

B The function will return 1 immediately

C The function will calculate factorial normally

D The function will return 0

Without a base case, recursion never stops, causing a stack overflow error.

Explain how a recursive function calculates the factorial of a number.

Think about how the problem is broken down into smaller parts.

Write the base case and recursive step for a factorial function in simple words.

Focus on what stops the recursion and what repeats.