java简单递归

Question

So there is a recursive method (can not use any loop), that has one parameter n, and the program will print out 2^n "*", for example, if n was 2, the output is ****, and if n was 3, the output is ********.

I'm stuck with this problem because I ran into some infinite recursion issues.

First I had this: but I soon realize that n will never reach the check.

↑↑↑ That was supposed to be n+1 (even though it doesn't work)

Then I tried this:

public class test {

    public static void main(String[] args) {
        printPowerOfTwoStars(3);

    }

    public static void printPowerOfTwoStars(int n){
        n = (int)Math.pow(2, n);
        if(n == 0){
            return;
        }
        else{
            System.out.print("*");
            printPowerOfTwoStars(n-1);
        }

    }

}

Ran into some infinite recursion again.

This seems like a simple program with simple logic, but I'm having trouble with the condition check, because what's being compared with n keeps changing.

How should I fix this problem?

Without using any helper method or creating any static variables.

Thank you

Answer 1

You need to use the fact that 2 to the power of n is just 2 to the power of n-1 , doubled. Your base case is that 2 to the power of 0 is 1.

public static void printPowerOfTwoStars(int n){
    if(n <= 0){
        System.out.print("*");
    }
    else{
        printPowerOfTwoStars(n-1);
        printPowerOfTwoStars(n-1);
    }
}