PHP Program to Print Pyramid Pattern

Use nested for loops in PHP to print spaces and stars for each row, like for ($i = 1; $i <= $rows; $i++) { for ($j = $rows; $j > $i; $j--) echo ' '; for ($k = 1; $k <= 2 * $i - 1; $k++) echo '*'; echo "\n"; } to print a pyramid pattern.

Examples

Input3

Output * *** *****

Input5

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

Input1

Output*

How to Think About It

To print a pyramid pattern, think of each row having spaces first, then stars. The number of spaces decreases each row, and the number of stars increases by two. Use one loop for rows, one loop for spaces, and one loop for stars.

Algorithm

1

Get the number of rows as input.

2

For each row from 1 to number of rows:

3

Print spaces equal to (total rows - current row).

4

Print stars equal to (2 * current row - 1).

5

Move to the next line after printing stars.

Code

php

<?php
$rows = 5;
for ($i = 1; $i <= $rows; $i++) {
    for ($j = $rows; $j > $i; $j--) {
        echo ' ';
    }
    for ($k = 1; $k <= 2 * $i - 1; $k++) {
        echo '*';
    }
    echo "\n";
}
?>

Output

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

Dry Run

Let's trace the pyramid pattern for 3 rows through the code.

1

Row 1

Spaces: 2 (because 3 - 1), Stars: 1 (2*1 - 1), Output: ' *'

2

Row 2

Spaces: 1 (3 - 2), Stars: 3 (2*2 - 1), Output: ' ***'

3

Row 3

Spaces: 0 (3 - 3), Stars: 5 (2*3 - 1), Output: '*****'

Row	Spaces	Stars	Output
1	2	1	*
2	1	3	***
3	0	5	*****

Why This Works

Step 1: Print spaces first

We print spaces first to push stars to the right, creating the pyramid shape. The spaces decrease each row using $rows - $i.

Step 2: Print stars next

Stars increase by two each row using 2 * $i - 1, making the pyramid wider as we go down.

Step 3: Move to next line

After printing spaces and stars for a row, we print a newline \n to start the next row below.

Alternative Approaches

Using while loops

php

<?php
$rows = 5;
$i = 1;
while ($i <= $rows) {
    $j = $rows;
    while ($j > $i) {
        echo ' ';
        $j--;
    }
    $k = 1;
    while ($k <= 2 * $i - 1) {
        echo '*';
        $k++;
    }
    echo "\n";
    $i++;
}
?>

Uses while loops instead of for loops; slightly longer but same logic.

Using str_repeat function

php

<?php
$rows = 5;
for ($i = 1; $i <= $rows; $i++) {
    echo str_repeat(' ', $rows - $i);
    echo str_repeat('*', 2 * $i - 1);
    echo "\n";
}
?>

Simplifies printing spaces and stars using built-in <code>str_repeat</code> function.

Complexity: O(n^2) time, O(1) space

Time Complexity

The program uses nested loops: one for rows and two inner loops for spaces and stars, each up to n, resulting in O(n^2) time.

Space Complexity

The program uses constant extra space for counters and prints directly, so space complexity is O(1).

Which Approach is Fastest?

Using str_repeat is more concise and may be slightly faster due to internal optimizations, but all approaches have similar O(n^2) time.

Approach	Time	Space	Best For
For loops	O(n^2)	O(1)	Clear control and beginner-friendly
While loops	O(n^2)	O(1)	Alternative loop style
str_repeat function	O(n^2)	O(1)	Concise and readable code