Valid Palindrome 2.java

class Solution
{
    //The function checks if a substring with given start and end points
    //is a palindrome or not.
    public boolean isPalindrome(String s, int start, int end)
    {
        while (start < end)
        {
            if (s.charAt(start) != s.charAt(end))
                return false;
            start++;
            end--;
        }
        return true;
    }

    public boolean validPalindrome(String s)
    {

        int start = 0, end = s.length() - 1;

        //while the two start and end pointers do not collide,
        //enter the while loop
        while (start < end)
        {
            //If two characters are equal, we move the start pointer forward
            //and the end pointer backward
            if (s.charAt(start) == s.charAt(end))
            {
                start++;
                end--;
            }
            //If the two characters are not equal, enters else
            else
            {
                //The if block checks whether or not a palindrome exists after deleting  
                //at most one character from the start or the end of the substring
                //by calling the isPalindrome function
                if (isPalindrome(s, start + 1, end) || isPalindrome(s, start, end - 1))
                    return true;

                //If it returns false, the string is not a palindrome
                return false;
            }
        }

        return true;
    }
}