Java中的空心方形分割模式

Question

I'm trying to create a program where you input an integer, and its output are hollowed square cells.. example output are shown below.

1 ↵

*

2 ↵

* * * 
* * * 
* * * 

3 ↵

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

4 ↵

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

And so on. Btw, here's where I am now.

int input = 4; // sample input
int sides;

sideL = input * input - (input - 1);

for (int a = 1; a <= sides; a++) {
  for (int b = 1; b <= sides; b++) {
    if (a == 1                 ||
      a == sides               ||
      a == sides / input + 1   ||
      a == sides / input + input ||
      b == 1                   ||
      b == sides               ||
      b == sides / input + 1   ||
      b == sides / input + input)
    {
      System.out.print("* ");
    } else {
        System.out.print("  ");
    }
  }
  System.out.println();
}

and it output

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

It continues with having 2 splits. What am I doing wrong?

Answer 1

Generally when you see multiple loops nested inside each other, you might think there's something wrong with the design. You can simplify the problem if you consider printing the big picture line-by-line. You have 2 kinds of lines:

• Border line (made full of stars)
• Inner line (which only has stars for the vertical columns)

So the main function should look something like this:

void hollowSquares(int number) {
    // Default cases
    if (number < 1) {
        return;
    }
    if (number == 1) {
        System.out.println("*");
        return;
    }
    
    // how many lines will be actually printed
    int numberOfLines = number * (number - 1) + 1;
    
    for (int i = 0; i < numberOfLines; i++) {
        if (isBorderLine(i, number)) {
            printBorderLine(numberOfLines);
        } else {
            printInnerLine(number);
        }
    }   
}

boolean isBorderLine(int line, int number) {
    return line % (number - 1) == 0;
}

So the only thing left to do is the actual printing. For the simpler case, border line, you repeat the star-and-space pattern:

void printBorderLine(int numberOfLines) {
    String line = String.join("", Collections.nCopies(numberOfLines, "* "));
    System.out.println(line);
}

For the inner border, you want to repeat the start-and-a-couple-spaces pattern, followed by a trailing star

void printInnerLine(int number) {
    int numberOfEmptySpaces = 2 * number - 3;
    String emptySpaces = String.join("", Collections.nCopies(numberOfEmptySpaces, " "));
    String starWithSpacesPattern = "*" + emptySpaces;
    String line = String.join("", Collections.nCopies(number, starWithSpacesPattern));
    line += "*"; // trailing star
    System.out.println(line);
}