How do I easily print number triangles? Using for loops :)

Question

I have a huge problem. I take Informatic class and we got a job to make a program that I have no idea how to make. Can you please help me?

Make a program in Java that will write this triangle in * if you put in an optional height that is written in the variable. The example if the number 4 is written looks like this:

      *
    * *
  * * *
* * * *

And if you have some more time can you please explain to me why did you do it like this? And how would you make this on paper?

Answer 1

I thought it might be fun to do it in one line:

public static void printTriangle(int size) {
    for (int i = 0; i < size; i++) System.out.println(Integer.toString(1 << (size - 1 - i), 2).replaceAll("^.", "").replaceAll(".", "  ") + Integer.toString(1 << i, 2).replaceAll(".", "* "));
}

Using bit-shifting kung fu and Integer.toString() with base 2 to produce a string of the required length.

---

Test code:

printTriangle(6);

Output:

          * 
        * * 
      * * * 
    * * * * 
  * * * * * 
* * * * * *