A palindrome is a word that reads the same way forward and backward, such as \"d

Question

A palindrome is a word that reads the same way forward and backward, such as "dad" or "deed". You can determine if a word is a palindrome using a stack as follows: 1. Determine the length, n, of the word w. 2. Push the first n/2 characters of w, one at a time, onto a stack s. Each character pushed onto s is removed from w. 3. If n is odd, remove the first character of w. 4. If s is empty, then stop and declare w to be a palindrome. 5. Now, compare the top character in s with the the first letter of what remains in w. If the letters are the same pop the top letter from s, remove the cooresponding letter from w and go back to step 4. If the letters are not the same, then stop and declare w to be a non-palindrome. Write a function called isPalindrome which uses a stack of characters to implement the above algorithm. Note, isPalindrome takes a single string paramenter w and returns true if w is a palindrome and returns false otherwise.

Explanation / Answer

import java.util.Scanner;
import java.util.Stack;

public class Palindrome {
   /**
   * creating instance of Stack
   */
   Stack<Character> s = new Stack<Character>();

   /**
   * isPalindrome method is checking for word is palindrome or not
   *
   * @param str
   */
   public void isPalindrome(String str) {
       /* creating instance of StringBuilder */
       StringBuilder word = new StringBuilder(str);
       /**
       * calculating length
       */
       int len = str.length();
       for (int i = 0; i < len / 2; i++) {
           /**
           * inserting into stack
           */
           s.push(str.charAt(i));
           /**
           * deleting character from word
           */
           word.deleteCharAt(i);
       }
       if (len % 2 == 0) {
           int index = 0;
           /**
           * checking character from word and popped from stack is same or not
           * if it is not same then print not palindrome and return
           */
           while (!s.isEmpty()) {
               if (!s.pop().equals(word.charAt(index))) {
                   System.out.println(str + " not a palindrome");
                   return;
               }
               index++;
           }
           System.out.println(str + " is a palindrome");
       } else {
           word.deleteCharAt(0);
           int index = 0;
           while (!s.isEmpty()) {
               if (!s.pop().equals(word.charAt(index))) {
                   System.out.println(str + " not a palindrome");
                   return;
               }
               index++;
           }
           System.out.println(str + " is a palindrome");
       }
   }

   public static void main(String[] args) {

       Scanner input = new Scanner(System.in);
       /**
       * Prompt for user input
       */
       System.out.println("Please Enter the word");
       String str = input.nextLine();
       Palindrome p = new Palindrome();
       /**
       * calling palindrome method
       */
       p.isPalindrome(str);

   }
}

/****************************output************************/

Please Enter the word
ded
ded is a palindrome

Please Enter the word
deed
deed is a palindrome

Thanks a lot

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