LeetCode 125: Valid Palindrome Solution

Master LeetCode problem 125 (Valid Palindrome), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

125. Valid Palindrome

Problem Explanation

Explanation

To solve this problem, we can use two pointers approach. We iterate through the string from both ends, moving towards the center, and compare alphanumeric characters. We skip non-alphanumeric characters during comparison. If at any point the characters don't match, we return false. If the loop completes without returning false, then the string is a valid palindrome.

  • Time complexity: O(n) where n is the length of the input string
  • Space complexity: O(1)

Solution Code

class Solution {
    public boolean isPalindrome(String s) {
        int left = 0, right = s.length() - 1;
        
        while (left < right) {
            char lChar = Character.toLowerCase(s.charAt(left));
            char rChar = Character.toLowerCase(s.charAt(right));
            
            if (!Character.isLetterOrDigit(lChar)) {
                left++;
            } else if (!Character.isLetterOrDigit(rChar)) {
                right--;
            } else {
                if (lChar != rChar) {
                    return false;
                }
                left++;
                right--;
            }
        }
        
        return true;
    }
}

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