Palindrome Detection in DSA Typescript - Build from Scratch

Palindrome Detection

📖 Scenario: You are building a simple program to check if a word is a palindrome. A palindrome is a word that reads the same forwards and backwards, like "level" or "radar".This is useful in games, puzzles, and text analysis.

🎯 Goal: Build a TypeScript program that checks if a given word is a palindrome and prints true if it is, or false if it is not.

📋 What You'll Learn

Create a string variable with a specific word

Create a helper variable to hold the reversed word

Write logic to reverse the string

Compare the original and reversed strings

Print the result as true or false

💡 Why This Matters

🌍 Real World

Palindrome detection is used in text processing, coding challenges, and games to find words or phrases that read the same forwards and backwards.

💼 Career

Understanding string manipulation and loops is fundamental for software development, especially in roles involving data processing, algorithms, and coding interviews.

1

Create the word variable

Create a string variable called word and set it to the exact value "racecar".

DSA Typescript

# Your code here

Hint

Use const to create a variable named word and assign the string "racecar".

2

Create a reversed word variable

Create a string variable called reversedWord and set it to an empty string "".

DSA Typescript

const word: string = "racecar";
# Your code here

Hint

Use let to create a variable named reversedWord and assign it an empty string.

3

Reverse the word using a loop

Use a for loop with a variable i starting from word.length - 1 down to 0. Inside the loop, add word[i] to reversedWord.

DSA Typescript

const word: string = "racecar";
let reversedWord: string = "";
# Your code here

Hint

Loop backwards over the string and add each character to reversedWord.

4

Compare and print the result

Print true if word is equal to reversedWord, otherwise print false. Use console.log(word === reversedWord).

DSA Typescript

const word: string = "racecar";
let reversedWord: string = "";
for (let i = word.length - 1; i >= 0; i--) {
    reversedWord += word[i];
}
# Your code here

Hint

Use console.log to print the comparison result of word === reversedWord.

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