A palindrome is a word, phrase, number, or other sequence of symbols or elements that reads the same forward or reversed.
For example: 12121 is palindrome as it reads same forward or reversed. madam is also a palindrome .
This is very simple interview question.There are many ways to check if given string is palindrome or not.
Reversing a String and then comparing it with input String:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 |
package org.arpit.java2blog; import java.util.Scanner; public class StringFullLoopPalindrome { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.print("Enter string : "); String str = scanner.nextLine(); String reverseStr = ""; for(int i = str.length() - 1; i >= 0; i--){ reverseStr = reverseStr + str.charAt(i); } if(str.equals(reverseStr)){ System.out.println("String is palindrome"); } else { System.out.println("String is not palindrome"); } } } |
Run above program, you will get following output:
|
1 2 3 4 5 6 |
Enter string : 12121 String is palindrome Enter a string : Apple String is not palindrome |
Using half loop,Moving from both end of String simultaneously:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 |
package org.arpit.java2blog; import java.util.Scanner; public class StringUsingHalfLoop { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.print("Enter a string : "); String str = scanner.nextLine(); boolean isPalin=isPalindrome(str); if(isPalin) System.out.println("String is Palindrome"); else System.out.println("String is not Palindrome"); } static boolean isPalindrome(String str) { for (int i = 0,j=str.length()-1; i <str.length()/2; i++,j--) { if(str.charAt(i)!=str.charAt(j)) { return false; } } return true; } } |
Run above program, you will get following output:
|
1 2 3 4 5 6 |
Enter a string : madam String is Palindrome Enter a string : adam String is not Palindrome |
Using StringBuilder’s reverse() function:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 |
package org.arpit.java2blog; import java.util.Scanner; public class StringPalindrome { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.print("Enter string : "); String str = scanner.nextLine(); StringBuilder strBuilder = new StringBuilder(str); strBuilder.reverse(); if(str.equals(strBuilder.toString())){ System.out.println("String is palindrome"); } else { System.out.println("String is not palindrome"); } } } |
Run above program, you will get following output:
|
1 2 3 4 5 6 |
Enter a string : stats String is palindrome Enter a string : 1212121 String is palindrome |
Please go through java interview programs for more such programs.
You can also check Python program to check if String is palindrome.
