PPractick

The problem

The symmetric void is a rectangle of stars with a diamond-shaped hole in the middle. The top half starts with a full row of stars, and a gap opens in the centre that widens by two each row. The bottom half closes it again. Each row has three segments (stars, gap, stars), and the challenge is writing the formulas for all three in both halves without off-by-one errors.

Example for n = 5:

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

Function signature

vector<string> symmetricVoid(int n);  // 2n rows, each 2n characters wide

Test cases

Input n	Output rows	Explanation
1	"**", "**"	Each half is one full row with no gap
2	"****", "* *", "* *", "****"	Gap of 2 in the middle rows
3	"******", "** **", "* *", "* *", "** **", "******"	Gap widens 0, 2, 4, then closes
5	as in the example	Every row is 2n = 10 characters

(Confirm: 2n rows, with the widest gap appearing twice. Every row is exactly 2n characters and ends with a star, so there are no trailing spaces.)

How interviewers phrase it

• "Print the symmetric void pattern for N."
• "Print a square of stars with a diamond-shaped hole in the centre."

Clarifying questions to ask

1. Is N the number of rows in each half?
2. Should the middle row repeat (2n rows)?
3. Print or return?

Follow-ups to expect

1. "What are the segment lengths in the top half?"
2. "And the bottom half?"
3. "How is this related to Pattern 20?"
4. "Complexity?"

Related questions

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

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