DSA interview question

Pattern 8: Inverted Star Pyramid

Easy · Algorithms · Topics: pattern building

The problem

Now turn the pyramid upside down: the first row is the widest (2n − 1 stars) and each row below loses a star on each side while gaining a leading space, until the last row has a single centred star. It tests whether you can derive formulas for a decreasing symmetric row, i − 1 spaces and 2(n − i) + 1 stars, instead of relying on the pyramid's formulas by memory.

Example for n = 3:

*****
 ***
  *

Function signature

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

Test cases

Input `n`	Output rows	Explanation
1	`"*"`	One star
2	`"**"`, `" "`	Widest row first
3	`"***"`, `" "`, `" "`	Spaces grow by one, stars shrink by two
4	`"*****"`, `" *"`, `" "`, `" "`

(Confirm: no trailing spaces; exactly n rows.)

How interviewers phrase it

"Print an inverted pyramid of stars."
"Print the pyramid upside down."

Clarifying questions to ask

Is N the number of rows?
Trailing spaces or not?
Print or return?

Follow-ups to expect

"How did you get 2(n − i) + 1?"
"Is there a simpler way?"
"What's the complexity?"

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