I'm trying to write a code that will output all possible passwords from a given array recursively, e.g. given the input

"ab"

will output the next:

a 
b 
aa
ab
ba
bb 

the problem is that I'm instructed to use only one loop in the crack() function below and that's it. I cannot use any other functions, just those two.

This is what I've got so far:

import java.util.*;

public class PasswordGen {

   public static void main(String[] args) {
    
     Scanner sc = new Scanner(System.in);
     System.out.println("Please enter a string:");
     char array[] = sc.next().toCharArray();
     System.out.println("All Combination:");

     crack(array);
    
     sc.close();
   }

   static void crack(char[] array) {        
     for (int i = 1; i <= array.length; i  ) {
        generate(array, i, "", array.length);
     }
   }

   static void generate(char[] array, int i, String string, int length) {
    
     //recursion stopping if condition is meet 
     if (i == 0) {
        System.out.println(string);
        return;
     }
    
     for (int j = 0; j < length; j  ) {         
        String charArray = string   array[j];
        generate(array, i -1, charArray , length);
     }
    
     return;
   }
}

Is there a way to get the same output without using the for loop in the generate() function? (see code below).

    static void generate(char[] array, int i, String string, int length) {
    
    //recursion stopping if condition is meet 
    if (i == 0) {
        System.out.println(string);
        return;
    }
    
    for (int j = 0; j < length; j  ) {
        
        String charArray = string   array[j];
        generate(array, i -1, charArray , length);
    }

Any suggestions/better way to do it?

CodePudding user response：

Not sure if this answers your question, but here is a class that does what you want without any for loop:

import java.util.*;
import java.util.stream.*;

class Bruteforcer {
    
    private List<Integer> state = Collections.singletonList(0);
    private final String allowedChars;
    private final Integer maxLength;
    
    public Bruteforcer(String allowedChars, Integer maxLength){
        
        assert allowedChars != null;
        assert allowedChars.length() > 0;
        assert maxLength > 0;
        
        this.allowedChars = allowedChars;
        this.maxLength = maxLength;
    }
    
    public String next(){
        
        final var allIndexesAreLastChar = this.state.stream().allMatch(i -> i == this.allowedChars.length() - 1);
        
        final var currentLength = this.state.size();
        
        if (currentLength > this.maxLength){
            return null;
        }
        
        final var nextPassword = this.state.stream()
            .map(i -> this.allowedChars.substring(i, i   1))
            .collect(Collectors.joining(""));
            
        if (allIndexesAreLastChar){
            this.state = Collections.nCopies(currentLength   1, 0);
            return nextPassword;
        }
        
        this.state = IntStream.range(0, currentLength)
            .mapToObj(i -> {
                
                final var current = this.state.get(currentLength - 1 - i);
                
                final var mustIncrement = i == 0 || this.state.get(currentLength - i) == this.allowedChars.length() - 1;
                
                if (mustIncrement){
                    return current == this.allowedChars.length() - 1 ? 0 : current   1;
                }
                
                return current;
            })
            .collect(Collectors.toList());
            
        Collections.reverse(this.state);
            
        return nextPassword;
    }
}

class FindPasswordApplication {
    public static void main(String[] args) {
        final var bruteforcer = new Bruteforcer("ab", 2);
        for (var i = 0; i < 10; i   ){
            final var password = bruteforcer.next();
            System.out.println(password);
        }
    }
}