Factorial Using Recursion in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this factorial function call?

Consider the following TypeScript code that calculates factorial using recursion. What will be printed when calling factorial(4)?

DSA Typescript

function factorial(n: number): number {
  if (n === 0) {
    return 1;
  }
  return n * factorial(n - 1);
}

console.log(factorial(4));

A 24

B 10

C 120

D 6

💡 Hint

Remember factorial of n is n * factorial of (n-1), and factorial of 0 is 1.

The factorial of 4 is 4 * 3 * 2 * 1 = 24. The function calls itself reducing n by 1 until it reaches 0, then returns 1.

❓ Predict Output

intermediate

What is the output of factorial(0)?

Using the same factorial function, what will be printed when calling factorial(0)?

DSA Typescript

function factorial(n: number): number {
  if (n === 0) {
    return 1;
  }
  return n * factorial(n - 1);
}

console.log(factorial(0));

A Error

B 0

C undefined

D 1

💡 Hint

Factorial of zero is defined as 1.

The base case returns 1 when n is 0, so factorial(0) returns 1.

🔧 Debug

advanced

What error does this factorial function cause?

Examine this factorial function. What error will occur when calling factorial(0)?

DSA Typescript

function factorial(n: number): number {
  if (n === 1) {
    return 1;
  }
  return n * factorial(n - 1);
}

console.log(factorial(0));

A Returns 6

B Returns 0

C Stack overflow error

D Syntax error

💡 Hint

Check the base case condition and what happens when n reaches 0.

The base case stops recursion only when n is 1. When n reaches 0, the function calls factorial(-1), then factorial(-2), and so on, causing infinite recursion and stack overflow.

🧠 Conceptual

advanced

How many times is factorial called when factorial(5) is executed?

Using the standard recursive factorial function, how many total calls to factorial are made when calculating factorial(5)?

DSA Typescript

function factorial(n: number): number {
  if (n === 0) {
    return 1;
  }
  return n * factorial(n - 1);
}

factorial(5);

A 5

B 6

C 4

D 1

💡 Hint

Count the initial call plus all recursive calls until base case.

The calls are factorial(5), factorial(4), factorial(3), factorial(2), factorial(1), factorial(0). Total 6 calls.

🚀 Application

expert

What is the output of this modified factorial function?

This factorial function prints the current value of n before the recursive call. What is the output when calling factorial(3)?

DSA Typescript

function factorial(n: number): number {
  if (n === 0) {
    return 1;
  }
  console.log(n);
  return n * factorial(n - 1);
}

factorial(3);

A [3, 2, 1]

B [1, 2, 3]

C [3, 2, 1, 0]

D [0, 1, 2, 3]

💡 Hint

The function prints before calling itself with n-1.

The function prints n starting from 3 down to 1 before reaching base case 0 which does not print.