Print a Reverse Star Pyramid

Easy10 min

Topics

BasicsPatternsLoops

Companies

TCSInfosysWipro

Given an integer n, return the n rows of an upside-down centered star pyramid — row i has (i − 1) leading spaces, then (2(n − i + 1) − 1) stars. This is the Full Star Pyramid, flipped: the widest row (2n − 1 stars, no spaces) comes first, shrinking by 2 stars — and gaining one leading space — each row after. Both solutions carry over the Full Star Pyramid's technique directly, just with (i − 1) and (2(n − i + 1) − 1) swapped in for the space and star counts.

Test Case 1:

Input:n = 4

Output:["*******", " *****", " ***", " *"]

Explanation:Row i has (i − 1) leading spaces, then (2(n − i + 1) − 1) stars.

Test Case 2:

Input:n = 1

Output:["*"]

Explanation:A single star, no spaces needed.

Constraints

◆1 ≤ n ≤ 20

Try the Dry Run

Mode

Approach

Approach & Solutions

Nested Loops — Spaces, Then StarsGood

For row i, first append (i − 1) spaces, then append (2(n − i + 1) − 1) stars. The upside-down version of the Full Star Pyramid: the widest row (all 2n − 1 stars, no spaces) comes first, shrinking by 2 stars — and gaining one leading space — each row after.

TimeO(n²)

SpaceO(n²) for the output

Java

Try it out

class Solution {
    public String[] printReverseStarPyramid(int n) {
        String[] result = new String[n];
        for (int i = 1; i <= n; i++) {
            StringBuilder row = new StringBuilder();
            for (int s = 1; s <= i - 1; s++) {
                row.append(' ');
            }
            for (int j = 1; j <= 2 * (n - i + 1) - 1; j++) {
                row.append('*');
            }
            result[i - 1] = row.toString();
        }
        return result;
    }
}

Built-in Repetition for Spaces and StarsOptimal

Build each half of the row with a built-in repeat: (i − 1) spaces concatenated with (2(n − i + 1) − 1) stars. C has no repeat built-in, so it keeps both loops.