Recursion vs Iteration When Each Wins in DSA Typescript - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate factorial using recursion.

DSA Typescript

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

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

An + 1

B1

Cn - 1

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n directly causes infinite recursion.

The recursive call must reduce the problem size by 1 each time, so n - 1 is correct.

2fill in blank

medium

Complete the code to calculate factorial using iteration.

DSA Typescript

function factorialIter(n: number): number {
  let result = 1;
  for (let i = 1; i <= [1]; i++) {
    result *= i;
  }
  return result;
}

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Aresult

Bn

Ci

Dn - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n - 1 excludes n from multiplication.

Using i or result in the condition causes errors.

The loop runs from 1 up to n, so the condition should be i <= n.

3fill in blank

hard

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

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'

A1

Bn + 1

Cn

Dn - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using n + 1 causes infinite recursion.

Using n directly causes infinite recursion.

The Fibonacci function calls fib(n-1) and fib(n-2) to reduce problem size correctly.

4fill in blank

hard

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

DSA Typescript

function sumToN(n: number): number {
  if (n === 0) {
    return 0;
  }
  return n [1] sumToN([2]);
}

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A+

B-

Cn - 1

Dn + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction instead of addition causes wrong results.

Using n + 1 causes infinite recursion.

To sum numbers from n down to 1, add n to sumToN(n - 1).

5fill in blank

hard

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

DSA Typescript

function reverseString(str: string): string {
  let reversed = '';
  for (let i = [1]; i [2] -1; i[3]) {
    reversed += str[i];
  }
  return reversed;
}

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Astr.length - 1

B>

C--

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 0 and incrementing causes no reversal.

Using '<' instead of '>' causes empty result.

The loop starts from the last index (length - 1), continues while i > -1, and decrements i each time.