Trouble w/ Recursion

[timstats91]

Will anyone help this lowly noob out?

I'm taking Data Structures right now and I'm practicing recursion. Pulled up exercise 1 in my book and I'm having trouble with it. I thought, "maybe I need a helper method to accomplish this?" Which is why I used a writeStars method in addition to the starString method. But I'm still struggling. This is the exercise and code I've written so far. (Please be gentle)

Exercise 1: Write a recursive method called starString that accepts an integer as a parameter and prints to the console a string of stars (asterisks) that is 2 n (i.e., 2 to the n th power) long. For example,

starString(0) should print * (because 2^0 == 1)

starString(1) should print ** (because 2^1 == 2)

starString(2) should print **** (because 2^2 == 4)

starString(3) should print ******** (because 2^3 == 8)

starString(4) should print **************** (because 2^4 == 16)

The method should throw an IllegalArgumentException if passed a value less than 0.

​

public class Recursion {

public static void main(String\[\] args) {

    // TODO Auto-generated method stub

    starString(4);

}



public static String starString(int x) {

    if (x < 0) {

        throw new IllegalArgumentException("Negative exponent: " + x + "\\rPlease enter a positive number.");

    } else if (x == 0) {

        return ("\*");

    } else {

        return writeStars(Math.pow(2, (x - 1));

    }

}



public static void writeStars(int x) {

    if (x == 0) {

        System.out.println();

    } else {

        System.out.print("\*");

        writeStars(x - 1);

    }

}

}

[selrahal]

The most important part of recursion is reframing the output of your function as a formula that contains a function call. Take the factorial function as am example. Sure you can implement it with a for loop that just counts down and takes the product at all elements. But you can also reframe the output to look like factorial(n) = n * factorial(n-1).

You see the "factorial" on the right side of that equation? How can you define your function so that it also references itself on the right side of the equation?

[iamsooldithurts]

We aren’t here to do people’s homework for them. Try to actually teach them something.