Valid Palindrome

Write a function that takes a string, s, as an input and determines whether or not it is a palindrome

Write a function that takes a string, s, as an input and determines whether or not it is a palindrome

Check if a String Is a Palindrome

Note

A palindrome is a word, phrase, or sequence of characters that reads the same backward as forward.

Constraints

• 1 ≤ s.length ≤ 2 × 10⁵
• The string s will only have English uppercase letters, lowercase letters, digits, and spaces.

Examples

Example 1

Input: ABCBA

Output: TRUE

Example 2

Input: ABCCA

Output: FALSE

Solution

This is an easy problem to solve using the two pointer method.

• We create two pointers: one starting at the left end of the string, and one starting at the right end.
• We compare the characters at both pointers:
  • If they are not the same, the string is not a palindrome. We return false right away.
  • If they match, we move the left pointer forward and the right pointer backward.
• We keep doing this until the two pointers meet or cross. If we get through the whole string without finding a mismatch, the string is a palindrome. We return true.

Code

function isPalindrome(s) {
    let left = 0,
        right = s.length - 1;

    while (left < right) {
        if (s[left] != s[right]) {
            return false;
        }
        left++;
        right--;
    }
    return true;
}

Complexity

• Time complexity: O(N)
• Space complexity: O(1)