Check if a String is a Palindrome

📌 Definition:

📖 Detailed Explanation:

Compare characters from both ends moving inward with two pointers — O(n) time, O(1) extra space. A common follow-up ignores case, spaces, and punctuation (a 'sentence palindrome').

💻 Solutions:

• JavaScript

function isPalindrome(s) {
  let i = 0, j = s.length - 1;
  while (i < j) {
    if (s[i] !== s[j]) return false;
    i++; j--;
  }
  return true;
}
// Sentence variant: normalize first
const isClean = (s) => {
  const c = s.toLowerCase().replace(/[^a-z0-9]/g, '');
  return c === [...c].reverse().join('');
};

🔑 Key Points:

• Two pointers from both ends → O(1) extra space
• Normalize case/whitespace for the sentence variant
• Empty and single-char strings are palindromes
• Avoid split-reverse-join when O(1) space matters

🌍 Real-World Example: