Palindrome Detection in DSA Javascript - Build from Scratch

Palindrome Detection

📖 Scenario: Imagine you are building a simple tool that checks if a word is a palindrome. A palindrome is a word that reads the same forwards and backwards, like "level" or "radar".This tool can help in word games or fun text analysis.

🎯 Goal: You will create a program that takes a word, checks if it is a palindrome, and prints the result.

📋 What You'll Learn

Create a variable called word with the exact string value "racecar".

Create a variable called reversedWord that holds the reversed version of word.

Create a variable called isPalindrome that is true if word and reversedWord are the same, otherwise false.

Print isPalindrome to show if the word is a palindrome.

💡 Why This Matters

🌍 Real World

Palindrome detection is useful in text analysis, word games, and coding challenges where recognizing symmetrical words or phrases matters.

💼 Career

Understanding string manipulation and comparison is fundamental in programming jobs, especially in roles involving data processing, software development, and algorithm design.

1

Create the word variable

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

DSA Javascript

// Your code here

Hint

Use const word = "racecar"; to create the variable.

2

Create the reversedWord variable

Create a variable called reversedWord that holds the reversed string of word. Use split(''), reverse(), and join('') methods.

DSA Javascript

const word = "racecar";
// Your code here

Hint

Split the word into letters, reverse the array, then join back to a string.

3

Check if the word is a palindrome

Create a variable called isPalindrome that is true if word equals reversedWord, otherwise false. Use the strict equality operator ===.

DSA Javascript

const word = "racecar";
const reversedWord = word.split('').reverse().join('');
// Your code here

Hint

Compare word and reversedWord using ===.

4

Print the palindrome check result

Print the value of isPalindrome using console.log(isPalindrome).

DSA Javascript

const word = "racecar";
const reversedWord = word.split('').reverse().join('');
const isPalindrome = word === reversedWord;
// Your code here

Hint

Use console.log(isPalindrome); to print the result.

Practice

1. What does a palindrome string mean in simple terms?

easy

A. A string that contains only vowels

B. A string that reads the same forwards and backwards

C. A string with all unique characters

D. A string that ends with a special character

Solution

1. Step 1: Understand palindrome definition

   A palindrome is a word or phrase that reads the same forwards and backwards, like 'madam' or 'racecar'.

2. Step 2: Compare options with definition

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

3. Final Answer:

   A string that 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 unique characters
• Thinking palindrome means only vowels
• Assuming palindrome ends with special character

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

easy

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

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

C. return str.length === 0;

D. return str.indexOf('a') !== -1;

Solution

1. Step 1: Understand palindrome check logic

   To check palindrome, reverse the string and compare with original.

2. Step 2: Analyze code snippets

   return str === str.split('').reverse().join(''); reverses the string and compares it correctly. Others do unrelated checks.

3. Final Answer:

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

4. Quick Check:

   Reverse and compare = return str === str.split('').reverse().join(''); [OK]

Hint: Reverse string and compare to original [OK]

Common Mistakes:

• Using toUpperCase instead of reversing
• Checking string length instead of content
• Searching for a character instead of palindrome

3. What will be the output of the following code?

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

medium

A. false

B. undefined

C. SyntaxError

D. true

Solution

1. Step 1: Normalize string by removing non-alphanumeric and lowercasing

   The string becomes 'amanaplanacanalpanama' after cleaning.

2. Step 2: Check if cleaned string equals its reverse

   Reversing 'amanaplanacanalpanama' gives the same string, so returns true.

3. Final Answer:

   true -> Option D

4. Quick Check:

   Clean and compare reversed string = true [OK]

Hint: Ignore case and non-letters, then compare reversed [OK]

Common Mistakes:

• Not removing spaces and punctuation
• Ignoring case differences
• Expecting false due to original formatting

4. Find the error in this palindrome check function:

function checkPalindrome(str) {
  for(let i = 0; i < str.length; i++) {
    if(str[i] !== str[str.length - i]) {
      return false;
    }
  }
  return true;
}

medium

A. Index for comparison should be str.length - i - 1

B. No error, function works correctly

C. Function should convert string to lowercase first

D. Loop should run only till half the string length

Solution

1. Step 1: Analyze index used for comparison

   Index str.length - i is off by one because string indices start at 0.

2. Step 2: Correct index calculation

   It should be str.length - i - 1 to compare correct characters from end.

3. Final Answer:

   Index for comparison should be str.length - i - 1 -> Option A

4. Quick Check:

   Off-by-one index error fixed by subtracting 1 [OK]

Hint: Remember last index is length - 1 [OK]

Common Mistakes:

• Using full length instead of half for loop
• Ignoring off-by-one in index
• Assuming case sensitivity causes error here

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

hard

A. Check if string length is even or odd first

B. Compare original string with reversed string directly

C. Remove non-alphanumeric characters, convert to lowercase, then compare with reversed string

D. Count vowels and consonants and compare counts

Solution

1. Step 1: Understand requirements for ignoring spaces, punctuation, and case

   We must clean the string by removing unwanted characters and normalize case.

2. Step 2: Choose approach that cleans and compares reversed string

   Remove non-alphanumeric characters, convert to lowercase, then compare with reversed string correctly removes non-alphanumeric characters, converts to lowercase, then compares reversed string.

3. Final Answer:

   Remove non-alphanumeric characters, convert to lowercase, then compare with reversed string -> Option C

4. Quick Check:

   Clean and compare reversed string for sentence palindrome [OK]

Hint: Clean string before palindrome check for sentences [OK]

Common Mistakes:

• Comparing raw strings with punctuation
• Ignoring case differences
• Using vowel/consonant counts which is unrelated