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 is to ignore case and non-alphanumeric characters ("A man, a plan, a canal: Panama").

💻 Solutions:

• Java
• JavaScript
• Python

public static boolean isPalindrome(String s) {
    int i = 0, j = s.length() - 1;
    while (i < j) {
        if (s.charAt(i++) != s.charAt(j--)) return false;
    }
    return true;
}

function isPalindrome(s) {
  let i = 0, j = s.length - 1;
  while (i < j) {
    if (s[i++] !== s[j--]) return false;
  }
  return true;
}

def is_palindrome(s):
    return s == s[::-1]

🔑 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
• Reverse-and-compare works but allocates a copy

🌍 Real-World Example: