Friday, June 9, 2023
HomeJava2 Methods to Examine if a String is Rotation of Different in...

2 Methods to Examine if a String is Rotation of Different in Java? Instance

Write a program to test if one String is a rotation of one other String is a standard coding downside you can see on programming job interviews.  A String is claimed to be a rotation of one other String, if it has the identical size, accommodates the identical characters, and so they had been rotated round one of many characters. For instance,  String“bcda” is a rotation of “abcd” however “bdca” isn’t a rotation of String “abcd”. One of many easiest options to this fascinating downside is first to test if two String has the identical size, if not then one String can’t be the rotation of one other. If they’re of the identical size then simply create one other String by concatenating first String with itself, now test if second String is a substring of this concatenated String or not, if sure, the second String is a rotation of first.

You could be questioning, how does this answer work? Properly, you possibly can rotate the String round some character and in case you be part of the String with itself then it truly accommodates all rotated model of itself. So, once you test the rotated string is a part of this concatenated String utilizing
accommodates() methodology, it returns true, whether it is, in any other case false.

Let’s perceive this with an instance, Suppose “JavaProgrammer” is first String and “ProgrammerJava” is second String. You’ll be able to rotate String round any character ranging from index 0, which is ‘J’ to index=length-1, which is ‘r’.

Now in case you concatenate “JavaProgrammer” with itself, you get “JavaProgrammerJavaProgrammer”, now you possibly can see that it accommodates each potential rotation of first string.

This is without doubt one of the excellent options and after I first discovered about it, I used to be as amazed as you are actually. Btw, if the interviewer will ask you easy methods to resolve this downside with out utilizing String concatenation then what do you do? Don’t be concerned I am going to present you ways to try this on this article.

And, in case you really feel you lack Information Construction and Algorithms expertise you possibly can revise them by becoming a member of Information Constructions and Algorithms: Deep Dive Utilizing Java course, top-of-the-line to be taught DS and Algorithms in Java.

2 Methods to Examine if a String is Rotation of Different in Java

Now that you’re aware of the issue and answer, together with how precisely this algorithm work, kind to write down code and resolve the issue in an expert manner.

Given two string s1 and s2 how will you test if s1 is a rotated model of s2?

As I stated, there are two methods to resolve this downside, first, is utilizing String concatenation and secondly is with out String concatenation.

The logic of Answer 1:

Listed below are the steps to test if a String is a rotation of one other String through the use of String concatenation:

  1. Concatenate two string s1 and s2 utilizing + operator. You may also use StringBuffer or StringBuilder if you wish to, however + appears to be like good and clear and it additionally makes use of StringBuilder internally (see Efficient Java).
  2. Examine if the rotated model is current within the concatenated model through the use of accommodates() methodology.

The logic of Answer 2:

Listed below are the steps to test if a given String s2 is the rotation of String s1 with out utilizing String concatenation.

  1. Examine if the size of each strings is similar or not, If not then they don’t seem to be rotation. If sure, then proceed to the following step.
  2. Examine if each Strings are equal, if sure then s2 is a rotation of s1. If not, then transfer to the following step.
  3. Take the primary string’s first character and discover the index within the second string. If not discovered, then it is not the rotation, but when discovered, proceed to the following step.
  4. Subtract the size of the rotated string with the index discovered to seek out the ultimate place.
  5. Examine if the primary character of the rotated String is similar because the character on the ultimate place of enter String and the enter.substring(finalPos) is the same as the rotated.substring(0, index) .

You need to use any answer to resolve the issue if there isn’t any restriction, however use the second answer if the Interviewer would not enable String concatenation. And, if you wish to be taught extra about recursive algorithms, it’s also possible to test Algorithms and Information Constructions – Half 1 and a couple of programs on Pluralsight.

Java Program to seek out if a given String is a Rotation of One other String

Right here is the whole Java program to test if each String are rotations of one another or not.

bundle dto;

 * Java Program to test if one String is rotation of different. On this program, we
 * will see two answer of this fascinating downside, one through the use of String
 * concatenation and different with out utilizing String concatenation.
 * @creator Javin

public class RotateStringDemo {

    public static void primary(String args[]) {
        String check = "abcd";
        String rotated = "dabc";

        boolean isRotated = isRotatedVersion(check, rotated);

        System.out.printf("Is '%s' is rotation of '%s' : %b %n", rotated, check,

     * Returns true if one string is rotation of one other, nulls should not
     * thought-about rotation of one another
     * @param str
     * @param rotated
     * @return true if rotated is rotation of String str
    public static boolean isRotatedVersion(String str, String rotated) {
        boolean isRotated = false;

        if (str == null || rotated == null) {
            return false;

        } else if (str.size() != rotated.size()) {
            isRotated = false;

        } else {
            String concatenated = str + str;
            isRotated = concatenated.accommodates(rotated);

        return isRotated;

     * Return true if rotated is rotation of enter String
     * @param enter
     * @param rotated
     * @return true if one String is rotation of different
    public static boolean isRotated(String enter, String rotated) {

        if (enter == null || rotated == null) {
            return false;

        } else if (enter.size() != rotated.size()) {
            return false;


        int index = rotated.indexOf(enter.charAt(0));
        if (index > -1) {

            if (enter.equalsIgnoreCase(rotated)) {
                return true;

            int finalPos = rotated.size() - index;
            return rotated.charAt(0) == enter.charAt(finalPos)
                    && enter.substring(finalPos).equals(
                            rotated.substring(0, index));
        return false;


Is 'dabc' is rotation of 'abcd' : true 

You’ll be able to see that fundamental check move, as given string “dabc” is a rotation of “abcd”, the place String is rotated across the letter “d”. 

Btw, if you’re making ready for coding interview or severe about enhancing coding ability then you possibly can additional see Grokking the Coding Interview: Patterns for Coding Questions to be taught extra about different widespread String and coding patterns like sliding window, merge interval, quick and sluggish pointers, and so forth which may help you to resolve 100+ leetcode issues and assist in a coding interview.

JUnit Checks

Listed below are some unit exams to confirm each variations of String rotation logic. That is written utilizing JUnit 4 library therefore you’ll want to embrace junit4.jar into your classpath to run these exams. The @Take a look at annotation is used to create check strategies, which shall be run by JUnit Runner. See JUnit in Motion to be taught extra about How JUnit works and The way it executes check circumstances.

public class StringRotateDemo {

    @Take a look at
    public void testIsRotatedVersion(){
        assertTrue(isRotatedVersion("abc", "bca"));
        assertTrue(isRotatedVersion("abc", "cab"));
        assertFalse(isRotatedVersion("abc", "bac"));
        assertFalse(isRotatedVersion("abc", null));
        assertFalse(isRotatedVersion("abc", ""));
    @Take a look at
    public void testisRotated(){
        assertTrue(isRotated("1234", "2341"));
        assertTrue(isRotated("1234", "3412"));
        assertTrue(isRotated("1234", "4123"));
        assertFalse(isRotated("1234", "23s41"));
        assertFalse(isRotated("1234", null));
        assertFalse(isRotated("1234", ""));

All check handed

right here is the screenshot which exhibits that each one JUnit check is passing and our code is working nice in many of the circumstances. You’ll be able to add extra unit exams if you wish to.

If you’re not snug with writing unit exams or lack creativeness and method to unit check your code, I recommend you to first learn the Take a look at-Pushed e book. It is without doubt one of the greatest books on unit testing and test-driven improvement and can train you easy methods to successfully check your code, each ideas, and instruments.

How to check if A String is rotation of other in Java?

That is all about easy methods to test if two String is rotations of one another in Java. The best answer is to simply concatenate each unique and rotated String and test if the rotation is current within the massive, joined String. That is an incredible answer as a result of once you be part of the unique and rotated model, it accommodates each single, potential rotation of the primary string. If the given rotation is current within the concatenated String, then it is undoubtedly within the rotation of given String.

Extra String Coding Issues For Apply

If you’re involved in fixing extra String primarily based algorithm issues then right here is the listing of a few of the steadily requested questions.

  • How one can Print duplicate characters from String? (answer)
  • How one can test if two Strings are anagrams of one another? (answer)
  • How one can program to print the primary non-repeated character from String? (answer)
  • How one can reverse String in Java utilizing Iteration and Recursion? (answer)
  • How one can test if a string accommodates solely digits?  (answer)
  • How one can discover duplicate characters in a String? (answer)
  • How one can rely the variety of vowels and consonants in a String? (answer)
  • How one can rely the incidence of a given character in String? (answer)
  • How one can convert numeric String to an int? (answer)
  • How one can discover all permutations of String? (answer)
  • 10 Algorithms Programs to Crack Programming Job Interviews (programs)
  • How one can reverse phrases in a sentence with out utilizing a library methodology? (answer)
  • How one can test if String is Palindrome? (answer)
  • How one can return the very best occurred character in a String? (answer)
  • How one can reverse a String in place in Java? (answer)
  • 50+ Information Construction and Algorithms Interview Questions (questions)
Thanks for studying this coding interview query thus far. For those who like this String interview query then please share it with your mates and colleagues. When you’ve got any questions or suggestions then please drop a remark.

P. S. – If you’re searching for some Free Algorithms programs to enhance your understanding of Information Construction and Algorithms, then you definitely also needs to test this listing of Free Information Construction and Algorithms Programs for Programmers. It accommodates the very best free on-line programs from Udemy, Pluralsight, and Coursera to be taught algorithms.



Please enter your comment!
Please enter your name here

Most Popular

Recent Comments