Looping Algorithm

Question

How do I make this:

*******
-*****-
--***--
---*---
--***--
-*****-
*******

The following is my code that I have written to try to accomplish the above, but it is not working as expected:

    public static void stars(/*int jmlBaris*/) {
    for ( int i = 7; i >= 1; i-=2) {
        for (int j = 1; j <= i; j++) {

            System.out.print("*");
        }
        System.out.println("");
    }

    for (int i = 1; i <= 7; i+=2) {
        for (int j = 1; j <= i; j++){
            System.out.print("*");
            }
        System.out.println("");
    }
}
public static void main(String[] args) {
    stars();
}
}

Answer 1

This is how I might write it.

// three loops
public static void stars(int size) {
    for (int y = 0; y < size; y++) {
        for (int i = 0; i < y && i < size - y - 1; i++)
            System.out.print(' ');
        for (int i = Math.min(y, size - y - 1); i < Math.max(y + 1, size - y); i++)
            System.out.print('*');
        System.out.println();
    }
}

or

// two loops
public static void stars(int size) {
    for (int y = 0; y < size; y++) {
        for (int x = 0; x < size; x++)
            System.out.print(
                    (x >= y && x < size - y) ||
                            (x >= size - y - 1 && x <= y) ? '*' : ' ');
        System.out.println();
    }
}

or

// one loop
public static void stars(int size) {
    for (int i = 0; i < size * size; i++) {
        int y = i / size, x = i % size;
        System.out.print(
                (x >= y && x < size - y) ||
                        (x >= size - y - 1 && x <= y) ? '*' : ' ');
        if (x == size - 1)
            System.out.println();
    }
}

Note: Whether this uses one, two or three loops, the time complexity is O(N^2). A simple way to determine this is the number of stars produced is O(N^2) no matter how it is done.

Answer 2

I would do something like this with substrings.

String a = "*******";  //7 stars
String blank = "        "; //7 spaces
int j = 7;
for (int i = 0; i < 7; i++) {
    if (i > j){
        System.out.print(blank.substring(0,i));
        System.out.println(a.substring(i,j));
        }
    else{
        System.out.print(blank.substring(0,j));
        System.out.println(a.substring(j,i));
        }
    j--;
}
System.out.println(a);

**Previous edit wouldn't have worked. Changes made.

This works.

Answer 3

Try something like this code I compiled on IDEOne (it seems to work, though): http://ideone.com/9xZ1YB

class Main
{
    public static void main(String[] args)
    {
        stars();
    }

    static void stars()
    {
        final int MAX_WIDTH = 7;

        for (int i = 0; i < 7; ++i)
        {
            int width;

            if (i < 3) width = MAX_WIDTH - i * 2;
            else if (i > 3) width = (i - 3) * 2 + 1;
            else width = 1;

            // Before spaces

            for (int j = 0; j < (MAX_WIDTH - width) / 2; ++j)
            {
                System.out.print(" ");
            }

            // Stars

            for (int j = 0; j < width; ++j)
            {
                System.out.print("*");
            }

            // After spaces

            for (int j = 0; j < (MAX_WIDTH - width) / 2; ++j)
            {
                System.out.print(" ");
            }

            System.out.println();
        }
    }
}