Why Recursion Exists and What Loops Cannot Express Cleanly in DSA Typescript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a recursive function that counts down from n to 1.

DSA Typescript

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

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

An - 1

Bn + 1

Cn

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n does not change the argument, causing infinite recursion.

The function calls itself with n - 1 to count down until it reaches 0.

2fill in blank

medium

Complete the code to calculate factorial of n recursively.

DSA Typescript

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

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An

B1

Cn + 1

Dn - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Returning n without recursion misses the factorial calculation.

Factorial multiplies n by factorial of n-1 until it reaches 1.

3fill in blank

hard

Fix the error in the recursive Fibonacci function to correctly compute fib(n).

DSA Typescript

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

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

An

Bn - 1

Cn + 1

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n or 1 as argument does not compute Fibonacci correctly.

The Fibonacci number is the sum of fib(n-1) and fib(n-2).

4fill in blank

hard

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

DSA Typescript

function sumTo(n: number): number {
  if (n === 1) return 1;
  return n [1] sumTo(n [2] 1);
}

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A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication or division instead of addition.

Not decreasing n causes infinite recursion.

The function adds n to the sum of numbers from 1 to n-1.

5fill in blank

hard

Fill all three blanks to create a recursive function that reverses a string.

DSA Typescript

function reverse(str: string): string {
  if (str.length <= 1) return str;
  return reverse(str[1]) [2] str[3];
}

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A.slice(1)

B+

C[0]

D.slice(0, 1)

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect slice indices.

Using multiplication instead of concatenation.

The function calls reverse on the string without the first character, then adds the first character at the end.