Java Program to Compute all the permutations of the string

Permutation of the string means all the possible new strings that can be formed by interchanging the position of the characters of the string. For example, string ABC has permutations [ABC, ACB, BAC, BCA, CAB, CBA].

Example: Java program to get all the permutation of a string

import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

class Main {
  public static Set<String> getPermutation(String str) {

    // create a set to avoid duplicate permutation
    Set<String> permutations = new HashSet<String>();

    // check if string is null
    if (str == null) {
      return null;
    } else if (str.length() == 0) {
      // terminating condition for recursion
      permutations.add("");
      return permutations;
    }

    // get the first character
    char first = str.charAt(0);

    // get the remaining substring
    String sub = str.substring(1);

    // make recursive call to getPermutation()
    Set<String> words = getPermutation(sub);

    // access each element from words
    for (String strNew : words) {
      for (int i = 0;i<=strNew.length();i++){

        // insert the permutation to the set
        permutations.add(strNew.substring(0, i) + first + strNew.substring(i));
      }
    }
    return permutations;
  }

  public static void main(String[] args) {

    // create an object of scanner class
    Scanner input = new Scanner(System.in);

    // take input from users
    System.out.print("Enter the string: ");
    String data = input.nextLine();
    System.out.println("Permutations of " + data + ": \n" + getPermutation(data));
    }
}

Output

Enter the string: ABC
Permutations of ABC: 
[ACB, BCA, ABC, CBA, BAC, CAB]

In Java, we have used the recursion to compute all the permutations of a string. Here, we store the permutation in a set. So, there will be no duplicate permutation.