How to find all permutation of a String in Java With Examples [Latest]

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.