Coding Interview Questions | Valid Palindrome

December 15th, 2023

Introduction:

This summary will talk about my solution to the valid palindrome problem as seen on leetcode here.

Solution:

function isPalindrome(s: string): boolean {
  const escapedString = s.replace(/[^A-Za-z0-9]/g, "").toLowerCase();

  // An empty string is by definition a palindrome
  if (!escapedString.length) {
    return true;
  }

  let forwardPointerIdx = 0;
  let endingPointerIdx = escapedString.length - 1;

  while (forwardPointerIdx < endingPointerIdx) {
    const forwardCharacter = escapedString[forwardPointerIdx];
    const endingCharacter = escapedString[endingPointerIdx];

    if (forwardCharacter !== endingCharacter) {
      return false;
    }

    forwardPointerIdx++;
    endingPointerIdx--;
  }
  return true;
}

Summary:

The solution above defines a function that checks if a given string is a palindrome. In order of steps completed:

1. It removes non-alphanumeric characters from the input string using a regular expression (/[^A-Za-z0-9]/g).
2. It converts the resulting string to lowercase.
3. If the processed string is empty, the function returns true as an empty string is considered a palindrome per the problem definition.
4. The function uses two pointers (forward and ending) to iterate through the characters of the processed string from both ends.
5. It compares the characters at the forward and ending positions. If they are not equal, the function returns false immediately.
6. If the loop completes without finding unequal characters, the function returns true, indicating that the string is a palindrome.