• Posted: 7 years ago
• Updated: 7 years ago
• 0 0
• Edit

A string is a palindrome if it can be read the same way in either forward or reverse direction. \( e.g \), `\( kayak \)'. It reads the same (\( k \) - \( a \) - \( y \) - \( a \) - \( k \)) from either direction. The algorithm works as :

• Initialize two pointers - one from the beginning of the string and the other from the end.
  
• Compare the characters in both the pointers until the first pointer is less than the second one.
  
• If they are same, increment the first pointer and decrement the second one.
  
• If they are not same, return false.
  

public boolean checkStringIsPalindrome(String input){

     /* Initialize first ponter */
     int pointer1 = 0;
     /* Initialize second ponter */
     int pointer2 = input.length - 1;

     while(pointer1  <  pointer2){
         /* check the characters at the two pointers */
         /* Ignore white space */
         if(input.charAt(pointer1) == ' ')
             pointer1++;
         if(input.charAt(pointer2) == ' ')
             pointer2--;

         /* If the characters at the two pointers does not match - Not a
         palindrome */
         if(input.charAt(pointer1) != input.charAt(pointer2)){
               return false;
               break;
         }else{  
               pointer1++;
               pointer2--;
         }
     }
     /* Yes, its a palindrome */
     return true;
 }

public boolean checkStringIsPalindrome(String input){
     for (int i = 0;i  <  input.length / 2) + 1; ++i){
        if (input.charAt(i) != input.charAt(input.length - i - 1))
        return false;
     }
     return true;
 }