[Algorithm] Solving Palindrome in 2 Ways

The best way to solve “Palindrome” challenge.

Target

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

function isPalindrome(string) {

}
isPalindrome("eye"); // return true

Example 1:

Input: "Madam, I'm Adam."
Output: true

Example 2:

Input: "race a car"
Output: false

Solution

Step 1

Convert all characters to lower case — ignoring cases

string.toLowerCase()

Step 2

Remove all non-alphanumeric characters — only alphanumeric characters

string.replace(/[^A-Za-z0-9]/g, '')
or
string.replace(/[\W_]/g, '')

\W is equivalent to [^A-Za-z0–9_]

Step 3

Reverse the string — it will match the original one if it is a palindrome

string.split('').reverse().join('')

Code

function isPalindrome(string) {
  const lowerString = string.toLowerCase();
  const characters = lowerString.replace(/[\W_]/g, '');
  const reverseCharacters = characters.split('').reverse().join('');
  return characters === reverseCharacters;
}
console.log(isPalindrome("Madam I'm Adam.")); // true
console.log(isPalindrome("race car")); // true
console.log(isPalindrome("Coding JavaScript")); // false

Using For … Loop

function isPalindrome(string) {
  const lowerString = string.toLowerCase();
  const characters = lowerString.replace(/[\W_]/g, '');
  const len = characters.length;
  for (var i = 0; i < len / 2; i++) {
     if (characters[i] !== characters[len - 1 - i]) return false;
  }
  return true;
}