is-a-palindrome.md

To solve the palindrome problem in JavaScript using map, reduce, and filter, we'll check whether a given string is a palindrome. A palindrome is a string that reads the same backward as forward.

Here's how we can achieve this using the mentioned array methods:

1. Normalize the string: Remove non-alphanumeric characters and convert it to lowercase.
2. Check for palindrome: Compare the string with its reversed version.

Solution

const isPalindrome = (str) => {
  // Normalize the string: remove non-alphanumeric characters and convert to lowercase
  const normalizedStr = str
    .toLowerCase()
    .split('')
    .filter(char => /[a-z0-9]/.test(char))
    .join('');

  // Reverse the normalized string
  const reversedStr = normalizedStr
    .split('')
    .reduce((acc, char) => char + acc, '');

  // Compare the normalized string with its reversed version
  return normalizedStr === reversedStr;
};

// Example usage
console.log(isPalindrome("A man, a plan, a canal, Panama")); // true
console.log(isPalindrome("racecar")); // true
console.log(isPalindrome("hello")); // false

Explanation

1. Normalization:

   • toLowerCase() is used to convert the string to lowercase.
   • split('') converts the string into an array of characters.
   • filter(char => /[a-z0-9]/.test(char)) filters out non-alphanumeric characters using a regular expression.
   • join('') joins the filtered characters back into a string.

2. Reversing the String:

   • split('') splits the normalized string into an array of characters.
   • reduce((acc, char) => char + acc, '') reverses the string by adding each character to the beginning of the accumulator.

3. Comparison:

   • The original normalized string is compared with its reversed version to determine if it is a palindrome.

Usage of map, reduce, filter:

• filter: Used to remove non-alphanumeric characters from the string.
• reduce: Used to reverse the string by accumulating characters in reverse order.

Notes