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// --- APPROACH 1: Using Built-in ---

function isPalindrome(str: string): boolean {
  const clean = str.toLowerCase().replace(/[^a-z0-9]/g, '');
  return clean === clean.split('').reverse().join('');
}
// Time: O(N) | Space: O(N)

// --- APPROACH 2: From Scratch (Two Pointers) ---

function isPalindrome(str: string): boolean {
  let left = 0, right = str.length - 1;
  while (left < right) {
    while (left < right && !isAlphaNum(str[left])) left++;
    while (left < right && !isAlphaNum(str[right])) right--;
    if (toLower(str[left]) !== toLower(str[right])) return false;
    left++; right--;
  }
  return true;
}
// Time: O(N) | Space: O(1) [Zero Extra Space]