Java Program to print distinct permutations of a string

Given a string str, the task is to print all the distinct permutations of str.
A permutation is an arrangement of all or part of a set of objects, with regard to the order of the arrangement.
For instance, the words ‘bat’ and ‘tab’ represents two distinct permutation (or arrangements) of a similar three letter word.

Examples:

Input: str = “abbb”
Output: [abbb, babb, bbab, bbba]

Input: str = “abc”
Output: [abc, bac, bca, acb, cab, cba]

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: Write a recursive function that will generate all the permutations of the string. Terminating condition will be when the passed string is empty, in that case the function will return an empty ArrayList. Before adding the generated string, just check if it has already been generated before to get the distinct permutations.

Below is the implementation of the above approach:

// Java implementation of the approach 
import java.util.ArrayList; 
  
public class GFG { 
  
    // Function that returns true if string s 
    // is present in the Arraylist 
    static boolean isPresent(String s, ArrayList<String> Res) 
    { 
  
        // If present then return true 
        for (String str : Res) { 
  
            if (str.equals(s)) 
                return true; 
        } 
  
        // Not present 
        return false; 
    } 
  
    // Function to return an ArrayList containg 
    // all the distinct permutations of the string 
    static ArrayList<String> distinctPermute(String str) 
    { 
  
        // If string is empty 
        if (str.length() == 0) { 
  
            // Return an empty arraylist 
            ArrayList<String> baseRes = new ArrayList<>(); 
            baseRes.add(""); 
            return baseRes; 
        } 
  
        // Take first character of str 
        char ch = str.charAt(0); 
  
        // Rest of the string after excluding 
        // the first character 
        String restStr = str.substring(1); 
  
        // Recurvise call 
        ArrayList<String> prevRes = distinctPermute(restStr); 
  
        // Store the generated sequence into 
        // the resultant Arraylist 
        ArrayList<String> Res = new ArrayList<>(); 
        for (String s : prevRes) { 
            for (int i = 0; i <= s.length(); i++) { 
                String f = s.substring(0, i) + ch + s.substring(i); 
  
                // If the generated string is not 
                // already present in the Arraylist 
                if (!isPresent(f, Res)) 
  
                    // Add the generated string to the Arraylist 
                    Res.add(f); 
            } 
        } 
  
        // Return the resultant arraylist 
        return Res; 
    } 
  
    // Driver code 
    public static void main(String[] args) 
    { 
        String s = "abbb"; 
        System.out.println(distinctPermute(s)); 
    } 
} 