Question

What does the method return: mystery(4,3)

public static int mystery(int x, int y){
if(y==1)
return x;
else
return x*mystery(x, y-1);
}



I watched some videos and read some tutorials online about recursions and I believe I understand, but what I don't understand is x*mystery(x,y-1)

What does that line of code even do? How do I times 4 by (4,2)?

Answer 1

It's a power function. It returns 4^3.
Think about it this way. Each time a recursive "instance" is called, it calls the function from the start. For the case mystery(4,3), this is more or less what happens:
First call: return 4*mystery(4,2)
Second call: return 4*4*mystery(4,1)
Third call: return 4*4*4 = 64.
The function will be called y times and also return 4 y times.

I may be able to write a clearer yet concise explanation of this recursive problem later on, but my brain is malfunctioning right now, my apologies :-)

Answer 2

you don't multiply 4 by (4,2), you multiply it by mystery(4,2).

So next you need to find out what mystery(4,2) returns.