Palindrome Detection with Text Reversal

What Is a Palindrome?

A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward. String reversal is the most intuitive way to detect palindromes.

Simple Palindrome Check

function isPalindrome(str) {
  const reversed = [...str].reverse().join("");
  return str === reversed;
}

Common Palindromes

Words: racecar, level, madam, radar, civic, kayak, rotor, noon, deed

Phrases (ignoring spaces and case):

• "A man a plan a canal Panama"
• "Was it a car or a cat I saw"
• "Never odd or even"
• "Do geese see God"

Normalization

For phrase palindromes, you need to normalize the text before comparing:

function isPalindromePhrase(str) {
  const normalized = str.toLowerCase().replace(/[^a-z0-9]/g, "");
  const reversed = [...normalized].reverse().join("");
  return normalized === reversed;
}

Steps:

1. Convert to lowercase
2. Remove all non-alphanumeric characters
3. Compare with the reversed version

Efficient Palindrome Check (Without Full Reversal)

You do not always need to reverse the entire string. A two-pointer approach is more efficient:

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

This approach is O(n) time and O(1) space — it checks characters from both ends without creating a new string.

Types of Palindromes

• Character palindrome: "racecar" (exact character reversal)
• Word palindrome: "Is it crazy how saying sentences backwards creates backwards sentences saying how crazy it is"
• Numeric palindrome: 12321, 1001, 9999