In this tutorial, we will learn how to find the permutation of a String in a Java Program. It’s a tricky question and asked mostly in Java interviews.
Algorithm for Permutation of a String in Java
We will first take the first character from the String and permute with the remaining chars. If String = “ABC” First char = A and remaining chars permutations are BC and CB. Now we can insert first char in the available positions in the permutations. BC -> ABC, BAC, BCA CB -> ACB, CAB, CBA We can write a recursive function to return the permutations and then another function to insert the first characters to get the complete list of permutations.
Java Program to Print Permutations of a String
package com.journaldev.java.string;
import java.util.HashSet;
import java.util.Set;
/**
* Java Program to find all permutations of a String
* @author Pankaj
*
*/
public class StringFindAllPermutations {
public static Set<String> permutationFinder(String str) {
Set<String> perm = new HashSet<String>();
//Handling error scenarios
if (str == null) {
return null;
} else if (str.length() == 0) {
perm.add("");
return perm;
}
char initial = str.charAt(0); // first character
String rem = str.substring(1); // Full string without first character
Set<String> words = permutationFinder(rem);
for (String strNew : words) {
for (int i = 0;i<=strNew.length();i++){
perm.add(charInsert(strNew, initial, i));
}
}
return perm;
}
public static String charInsert(String str, char c, int j) {
String begin = str.substring(0, j);
String end = str.substring(j);
return begin + c + end;
}
public static void main(String[] args) {
String s = "AAC";
String s1 = "ABC";
String s2 = "ABCD";
System.out.println("\nPermutations for " + s + " are: \n" + permutationFinder(s));
System.out.println("\nPermutations for " + s1 + " are: \n" + permutationFinder(s1));
System.out.println("\nPermutations for " + s2 + " are: \n" + permutationFinder(s2));
}
}
I have used Set to store the string permutations. So that duplicates are removed automatically.
Output
Permutations for AAC are:
[AAC, ACA, CAA]
Permutations for ABC are:
[ACB, ABC, BCA, CBA, CAB, BAC]
Permutations for ABCD are:
[DABC, CADB, BCAD, DBAC, BACD, ABCD, ABDC, DCBA, ADBC, ADCB, CBDA, CBAD, DACB, ACBD, CDBA, CDAB, DCAB, ACDB, DBCA, BDAC, CABD, BADC, BCDA, BDCA]
That’s all for finding all permutations of a String in Java.
You can download the example program code from our GitHub Repository.
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About the author
Java and Python Developer for 20+ years, Open Source Enthusiast, Founder of https://www.askpython.com/, https://www.linuxfordevices.com/, and JournalDev.com (acquired by DigitalOcean). Passionate about writing technical articles and sharing knowledge with others. Love Java, Python, Unix and related technologies. Follow my X @PankajWebDev
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