Java - Hourglass

Question

I am missing just a little bit. What I want:

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

What i get

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

Code

public class HD404 {
    public static void main(String[] args) {

        int N = StdIn.readInt();
        int x = N*2-1;

        for (int i = 0; i < N; i++) {
            for (int j = i; j > 0; j--) {
                StdOut.print(" ");
            }
            for (int k = 0; k < x; k++) {
                StdOut.print("*");
            }
            x-=2;
            StdOut.println();
        }

        x = 1;
        for (int i = 0; i < N; i++) {
            for (int j = i; j < N-1; j++) {
                StdOut.print(" ");
            }
            for (int k = 0; k < x; k++) {
                StdOut.print("*");
            }
            x += 2;
            StdOut.println();
        }

    }
}

Now I'm just guessing, and I just can’t indicate my mistake. What am I missing here?

Answer 1

The problems lie with the second part of your code, where you ask to draw one star, and you start from scratch, where you have to start from one.

---

Decision

x = 1;
for (int i = 0; i < N; i++)

should be replaced by

x = 3;
for (int i = 1; i < N; i++)

Answer 2

The problem is that you start to draw the bottom of the hourglass with 1 asterisk ( x = 1) instead of 3.

, N-2, N-1, 1 0. , .

:

public static void main(String[] args) {

    int N = StdIn.readInt();
    int x = N*2-1;

    for (int i = 0; i < N; i++) {
        for (int j = i; j > 0; j--) {
            StdOut.print(" ");
        }
        for (int k = 0; k < x; k++) {
            StdOut.print("*");
        }
        x-=2;
        StdOut.println();
    }

    x = 3; // <-- not 1 here, the first line has 3 asterisks
    for (int i = 1; i < N; i++) { // <-- i starts at 1 because the first line was already drawn in the upper half
        for (int j = i; j < N-1; j++) {
            StdOut.print(" ");
        }
        for (int k = 0; k < x; k++) {
            StdOut.print("*");
        }
        x += 2;
        StdOut.println();
    }

}

---

, :

• x , 0 x ( ) ,
• x , , *.
• * , min(i, x-i) max(i, x-i) ( , i < x-i , i > x-i).

:

public static void main(String[] args) {
    int N = 4;
    int x = 2 * N - 1;

    for (int i = 0; i <= x; i++) {
        if (i == N) continue; // skip the middle-line for it not to be drawn twice
        for (int j = 0; j < x; j++) {
            System.out.print(j >= Math.min(i, x-i) && j < Math.max(i, x-i) ? "*" : " ");
        }
        System.out.println();
    }
}

:

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

Answer 3

The easiest way I can come up with is probably to prevent the last iteration of your first outer loop, so you prevent the first single line from appearing.

I would do this:

for(int i = 0; i < N && x > 1; i++)
{
    /*Code of the first inner loop*/
}