JavaScript Program to Print Pyramid Pattern

Use nested for loops in JavaScript to print a pyramid pattern by printing spaces and stars in each line, like for(let i=1; i<=n; i++){ let row = ' '.repeat(n-i) + '* '.repeat(i); console.log(row); }.

Examples

Input3

Output * * * * * *

Input5

Output * * * * * * * * * * * * * * *

Input1

Output*

How to Think About It

To print a pyramid pattern, think of each line as having some spaces followed by stars. The number of spaces decreases each line, and the number of stars increases. Use one loop to go through each line and inside it, print spaces first, then stars.

Algorithm

1

Get the number of rows (n) for the pyramid.

2

For each line from 1 to n:

3

Calculate and print (n - current line) spaces.

4

Print stars equal to the current line number, each followed by a space.

5

Move to the next line and repeat until all lines are printed.

Code

javascript

const n = 5;
for (let i = 1; i <= n; i++) {
  let row = ' '.repeat(n - i) + '* '.repeat(i);
  console.log(row);
}

Output

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

Dry Run

Let's trace the pyramid printing for n=3 through the code

1

First line (i=1)

Print 2 spaces and 1 star: ' * '

2

Second line (i=2)

Print 1 space and 2 stars: ' * * '

3

Third line (i=3)

Print 0 spaces and 3 stars: '* * * '

i	Spaces	Stars	Row Output
1	2	1	*
2	1	2	* *
3	0	3	* * *

Why This Works

Step 1: Spaces decrease each line

We print n - i spaces to push stars to the right, creating the pyramid shape.

Step 2: Stars increase each line

We print i stars with spaces after each to form the pyramid's width.

Step 3: Use of nested repetition

Using repeat() makes printing spaces and stars simple and clean.

Alternative Approaches

Using nested for loops

javascript

const n = 5;
for(let i = 1; i <= n; i++) {
  let row = '';
  for(let j = 1; j <= n - i; j++) {
    row += ' ';
  }
  for(let k = 1; k <= i; k++) {
    row += '* ';
  }
  console.log(row);
}

This approach uses explicit loops for spaces and stars, which is more verbose but clear for beginners.

Using Array fill and join

javascript

const n = 5;
for(let i = 1; i <= n; i++) {
  const spaces = Array(n - i).fill(' ').join('');
  const stars = Array(i).fill('* ').join('');
  console.log(spaces + stars);
}

This uses arrays to build strings, which can be more flexible but slightly more complex.

Complexity: O(n^2) time, O(n) space

Time Complexity

The program uses nested loops: one for each line and one for printing stars/spaces, resulting in O(n^2) time.

Space Complexity

The extra space is mainly for the string holding each line, which is O(n) in length.

Which Approach is Fastest?

Using String.repeat() is generally faster and cleaner than nested loops for building strings.

Approach	Time	Space	Best For
String.repeat()	O(n^2)	O(n)	Clean and efficient string building
Nested for loops	O(n^2)	O(n)	Clear logic for beginners
Array fill and join	O(n^2)	O(n)	Flexible string construction