Recursion Concept and Call Stack Visualization in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the function call itself recursively.

DSA Typescript

function factorial(n: number): number {
  if (n <= 1) return 1;
  return n * factorial([1]);
}

Drag options to blanks, or click blank then click option'

An + 1

Bn - 1

C1

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n directly does not reduce the problem size.

The function calls itself with n - 1 to reduce the problem size until it reaches the base case.

2fill in blank

medium

Complete the code to correctly calculate the sum of numbers from 1 to n using recursion.

DSA Typescript

function sumToN(n: number): number {
  if (n === 1) return 1;
  return n + sumToN([1]);
}

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An - 1

B1

Cn + 1

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n directly does not reduce the problem size.

The function calls itself with n - 1 to add all numbers down to 1.

3fill in blank

hard

Fix the error in the recursive Fibonacci function to avoid infinite recursion.

DSA Typescript

function fibonacci(n: number): number {
  if (n <= 1) return n;
  return fibonacci([1]) + fibonacci(n - 2);
}

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An - 1

B1

Cn - 2

Dn + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using the same argument twice does not reduce the problem.

The function must call fibonacci with n - 1 and n - 2 to correctly compute the Fibonacci sequence.

4fill in blank

hard

Fill both blanks to create a recursive function that prints numbers from n down to 1.

DSA Typescript

function printDown(n: number): void {
  if (n === 0) return;
  console.log([1]);
  printDown([2]);
}

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An

Bn - 1

Cn + 1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Printing n - 1 before calling printDown causes off-by-one errors.

Calling printDown with n + 1 causes infinite recursion.

The function prints the current number n and then calls itself with n - 1 to count down.

5fill in blank

hard

Fill both blanks to create a recursive function that builds an array of numbers from 1 to n.

DSA Typescript

function buildArray(n: number): number[] {
  if (n === 0) return [];
  const arr = buildArray([1]);
  arr.push([2]);
  return arr;
}

Drag options to blanks, or click blank then click option'

An - 1

Bn

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Pushing 1 every time instead of n causes incorrect arrays.

Calling buildArray with n + 1 causes infinite recursion.

The function calls itself with n - 1 to build the smaller array, then adds n to the end. The base case returns an empty array when n is 0.