Palindrome Detection in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to reverse the string.

DSA Typescript

const reversed = str[1]('').reverse().join('');

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

Asplit

BtoUpperCase

Ctrim

Dconcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using toUpperCase() instead of split()

Trying to reverse the string without converting to array

We use split('') to convert the string into an array of characters so that reverse() can be applied.

2fill in blank

medium

Complete the code to check if the string is equal to its reverse.

DSA Typescript

return str === [1];

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Astr.split('')

Bstr.toLowerCase()

Creversed

Dstr.length

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with str.length instead of reversed string

Using str.toLowerCase() without reversing

We compare the original string with the reversed string to check for palindrome.

3fill in blank

hard

Fix the error in the function to ignore case when checking palindrome.

DSA Typescript

const normalized = str[1]();

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

AtoLowerCase

BtoUpperCase

Ctrim

Dsplit

Attempts:

3 left

💡 Hint

Common Mistakes

Using toUpperCase() which also works but is not the chosen answer here

Using trim() which only removes spaces

toLowerCase() converts all letters to lowercase so case differences don't affect palindrome check.

4fill in blank

hard

Fill both blanks to remove spaces and check palindrome ignoring spaces.

DSA Typescript

const normalized = str[1](/\s+/g, '').toLowerCase();
const reversed = normalized[2]('').reverse().join('');

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

Areplace

Bsplit

Ctrim

Dconcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using trim() which only removes spaces at start/end

Using concat which does not remove spaces

We use replace to remove all spaces and split to convert string to array for reversing.

5fill in blank

hard

Fill all three blanks to create a function that returns true if input is palindrome ignoring case and spaces.

DSA Typescript

function isPalindrome(str: string): boolean {
  const normalized = str[1](/\s+/g, '').[2]();
  const reversed = normalized[3]('').reverse().join('');
  return normalized === reversed;
}

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

Areplace

BtoLowerCase

Csplit

Dtrim

Attempts:

3 left

💡 Hint

Common Mistakes

Using trim instead of replace to remove all spaces

Not converting to lowercase before checking

Not splitting string before reversing

We remove spaces with replace, convert to lowercase with toLowerCase, and split to array before reversing.

Practice

1. What does it mean if a string is a palindrome?

easy

A. The string has no spaces

B. The string reads the same forwards and backwards

C. The string contains only letters

D. The string is all uppercase

Solution

1. Step 1: Understand palindrome definition

   A palindrome is a word or phrase that reads the same forwards and backwards.

2. Step 2: Compare options with definition

   Only The string reads the same forwards and backwards matches this definition exactly.

3. Final Answer:

   The string reads the same forwards and backwards -> Option B

4. Quick Check:

   Palindrome = same forwards and backwards [OK]

Hint: Palindrome means same forwards and backwards [OK]

Common Mistakes:

• Confusing palindrome with uppercase or letter-only strings
• Thinking palindrome means no spaces
• Assuming palindrome means all lowercase

2. Which of the following TypeScript code snippets correctly checks if a string str is a palindrome?

easy

A. return str === str.split().reverse().join();

B. return str === str.reverse();

C. return str === str.split('').reverse().join('');

D. return str === str.split('').reverse();

Solution

1. Step 1: Understand string reversal in TypeScript

   To reverse a string, split it into characters, reverse the array, then join back.

2. Step 2: Check each option's correctness

   return str === str.split('').reverse().join(''); uses split(''), reverse(), join('') correctly. Others miss correct methods or arguments.

3. Final Answer:

   return str === str.split('').reverse().join(''); -> Option C

4. Quick Check:

   Correct string reversal syntax = return str === str.split('').reverse().join(''); [OK]

Hint: Use split(''), reverse(), join('') to reverse strings [OK]

Common Mistakes:

• Using reverse() directly on string (not an array)
• Using split() without arguments returns whole string as one element
• Forgetting to join array back to string

3. What will be the output of this TypeScript code?

function isPalindrome(s: string): boolean {
  const cleaned = s.toLowerCase().replace(/[^a-z0-9]/g, '');
  return cleaned === cleaned.split('').reverse().join('');
}
console.log(isPalindrome('A man, a plan, a canal: Panama'));

medium

A. true

B. false

C. SyntaxError

D. undefined

Solution

1. Step 1: Clean the string

   The string is converted to lowercase and non-alphanumeric characters removed, resulting in 'amanaplanacanalpanama'.

2. Step 2: Check palindrome condition

   This cleaned string equals its reverse, so function returns true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   Cleaned string equals reversed = true [OK]

Hint: Clean string before checking palindrome for accurate result [OK]

Common Mistakes:

• Not cleaning string before palindrome check
• Assuming spaces or punctuation affect palindrome
• Confusing true/false output

4. Find the error in this palindrome check function:

function checkPalindrome(str: string): boolean {
  const reversed = str.split('').reverse();
  return str === reversed;
}

medium

A. reverse() does not work on strings

B. Function missing return type

C. split('') is incorrect usage

D. reversed is an array, not a string

Solution

1. Step 1: Analyze reversed variable type

   reversed is an array after split and reverse, not a string.

2. Step 2: Compare string with array

   Comparing string to array returns false always; need to join array back to string.

3. Final Answer:

   reversed is an array, not a string -> Option D

4. Quick Check:

   Compare string to string, not array [OK]

Hint: Join reversed array back to string before comparing [OK]

Common Mistakes:

• Comparing string directly to array
• Forgetting to join reversed array
• Assuming split('') returns string

5. You want to check if a sentence is a palindrome ignoring spaces, punctuation, and case. Which approach is best?

hard

A. Convert to lowercase, remove non-alphanumeric chars, then compare with reversed

B. Compare original string with reversed string directly

C. Remove spaces only, then compare

D. Convert to uppercase and compare with reversed uppercase

Solution

1. Step 1: Understand palindrome ignoring spaces and punctuation

   We must clean the string by removing spaces and punctuation and normalize case.

2. Step 2: Choose correct cleaning and comparison

   Convert to lowercase, remove non-alphanumeric chars, then compare with reversed cleans string by removing non-alphanumeric characters and lowercases it before comparing with reversed.

3. Final Answer:

   Convert to lowercase, remove non-alphanumeric chars, then compare with reversed -> Option A

4. Quick Check:

   Clean and normalize before palindrome check [OK]

Hint: Clean string fully before palindrome check for accuracy [OK]

Common Mistakes:

• Only removing spaces but not punctuation
• Comparing without case normalization
• Assuming uppercase conversion alone is enough