PPractick

The problem

The college coding club prints a logo on its welcome screen: a hollow diamond made of stars, with stars only on the outline and spaces inside. The club secretary wants it generated for any size n, where n is the number of rows from the top point down to the widest row. This pattern is a good "hard" exercise because it combines three ideas from easier patterns: leading spaces that shrink row by row, an inside gap that grows, and a mirrored bottom half that must not repeat the middle row.

Example for n = 4:

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

Function signature

vector<string> hollowDiamond(int n);  // 2n - 1 rows, leading spaces included, no trailing spaces

Test cases

Input n	Output rows	Explanation
1	"*"	A single star
2	" *", "* *", " *"	Middle row has a 1-space gap
3	" *", " * *", "* *", " * *", " *"	Gap grows 1, 3
4	7 rows as in the example	Gap grows 1, 3, 5; bottom mirrors top without repeating the widest row

(Confirm: the output has 2n − 1 rows; the first and last rows have a single star; rows have no trailing spaces.)

How interviewers phrase it

• "Print a hollow diamond of stars for a given N," usually drawn for N = 4 or 5.
• Asked after a solid diamond, as a harder variant: "Now make only the border visible."
• Sometimes phrased as a "draw the shape" question in campus assessments with an exact output checker.

Clarifying questions to ask

1. Does N mean the number of rows in the top half (including the widest row), or the total height?
2. Should rows have trailing spaces to make a perfect rectangle, or end at the last star?
3. Should I print directly or return the rows?
4. What should happen for N = 1?

Follow-ups to expect

1. "How did you work out the gap size?"
2. "Why doesn't the first row have two stars?"
3. "How do you avoid printing the middle row twice?"
4. "How would you make it solid?"
5. "What's the complexity?"

Related questions

• Easy and Medium Easy
• Pattern 1 Easy
• Pattern 2 Easy
• Pattern 3 Easy
• Pattern 4 Easy
• Pattern 5 Easy

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