PPractick

The problem

The pyramid is the first pattern where each row needs two segments: leading spaces to centre it, then the stars. Row 1 has one star in the middle, and each row below adds a star on each side. It's the pattern that teaches you to derive two formulas per row, one for the spaces (n − i) and one for the stars (2i − 1). Almost every later symmetric pattern (diamonds, hills, crowns) is built on this one.

Example for n = 3:

  *
 ***
*****

Function signature

vector<string> starPyramid(int n);  // row i: n - i spaces, then 2i - 1 stars

Test cases

Input n	Output rows	Explanation
1	"*"	One star, no spaces
2	" *", "***"	Row 1 has one leading space
3	" *", " ***", "*****"	Stars grow by two, spaces shrink by one
4	" *", " ***", " *****", "*******"	Last row has 2n − 1 stars

(Confirm: rows have leading spaces for centring but no trailing spaces; some judges also print trailing spaces to make each row 2n − 1 wide.)

How interviewers phrase it

• "Print a pyramid of stars of height N."
• One of the most common pattern questions in campus placements, often followed by "now print it upside down" and "now print a diamond".

Clarifying questions to ask

1. Is N the height (number of rows)?
2. Should rows include trailing spaces?
3. Print or return?

Follow-ups to expect

1. "How did you get 2i − 1 stars?"
2. "And n − i spaces?"
3. "How wide is the last row?"
4. "How do you invert it?"
5. "What's the 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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