Question

Write a program using java that determines whether an input string is a palindrome; that is, whether it can be read the same way forward and backward. At each point, you can read only one character of the input string; do not use an array to first store this string and then analyze it (except, possibly, in a stack implementation). Consider using multiple stacks.

please type out the code :)

Answer 1

import java.util.Scanner;
import java.util.Stack;
public class PalindromeStack {
  private static boolean isPalindrome(String str){
    int len = str.length();
    char temp;
    int i;
    str = str.toLowerCase();
    Stack<Character> stack = new Stack<Character>();
    for (i = 0; i < len; i++) {
      temp = str.charAt(i);
      if(temp>='a' && temp<='z') {
        stack.push(temp);
      }
    }
    i = 0;
    while (i<str.length()){
      temp = str.charAt(i);
      if(temp>='a' && temp<='z') {
        if (stack.pop() != str.charAt(i)) {
          return false;
        }
      }
      i++;
    }
    return true;
  }

  public static void main(String args[]){
    Scanner scanner = new Scanner(System.in);
    System.out.print("Enter a string: ");
    String str = scanner.nextLine();
    if (isPalindrome(str)) {
      System.out.println("It is a palindrome!");
    } else {
      System.out.println("It is NOT a palindrome!");
    }

  }
}