public class Solution {
 public boolean isPalindrome(String s) {
 int i = 0;
 int j = s.length() - 1;
 boolean res = true;
 while (res) {
 // Iterates through string to find first char which is alphanumeric.
 // Done to ignore non-alphanumeric characters.
 // Starts from 0 to j-1.
 while (i < j && isNotAlphaNumeric(s.charAt(i))) {
 i++;
 }
 // Similarly from j-1 to 0.
 while (i < j && isNotAlphaNumeric(s.charAt(j))) {
 j--;
 }
 // Checks if i is greater than or equal to j.
 // The main loop only needs to loop n / 2 times hence this condition (where n is string
 // length).
 if (i >= j) {
 break;
 }
 // Assigning found indices to variables.
 // The upperToLower function is used to convert characters, if upper case, to lower
 // case.
 // If already lower case, it'll return as it is.
 char left = upperToLower(s.charAt(i));
 char right = upperToLower(s.charAt(j));
 // If both variables are not same, result becomes false, and breaks out of the loop at
 // next iteration.
 if (left != right) {
 res = false;
 }
 i++;
 j--;
 }
 return res;
 }
 private boolean isNotAlphaNumeric(char c) {
 return (c < 'a' || c > 'z') && (c < 'A' || c > 'Z') && (c < '0' || c > '9');
 }
 private boolean isUpper(char c) {
 return c >= 'A' && c <= 'Z';
 }
 private char upperToLower(char c) {
 if (isUpper(c)) {
 c = (char) (c + 32);
 }
 return c;
 }
}