PHP Number Diamond Pattern

Beginner
5 min read
Updated: Sep 2026
3 programs
Live preview
Centered number diamond 1, 123, 12345, 123456789 in PHP programming
Definition

What Is This Pattern?

A number diamond prints ascending digits in odd-length rows that grow to a peak, then shrink back — centered with leading spaces.

Remember
Rule: top 1..levels, bottom levels-1..1; each row prints 1..(2*i-1)

    1
   123
  12345
 1234567
123456789
 1234567
  12345
   123
    1   ← levels = 5

In PHP use two outer loops: grow $i to $levels, then shrink. Indent with spaces, then print $k from 1 while $k < $i * 2.

Approach

How to Solve It

Build the top half, then mirror it downward — spaces first, then digits.

MethodIdeaBest for
Two-half diamondTop 1..$levels, bottom $levels-1..1Learning, interviews, exams
Levels inputSame logic with a user-chosen $levelsPractice / demos

Pseudocode

Pseudocode
for i from 1 to levels:
    print (levels - i) spaces
    print digits 1 to (2*i - 1)
    print newline
for i from levels-1 down to 1:
    print (levels - i) spaces
    print digits 1 to (2*i - 1)
    print newline

Cheat sheet

GoalPattern
Top halffor ($i = 1; $i <= $levels; $i++)
Bottom halffor ($i = $levels - 1; $i >= 1; $i--)
Top indentfor ($j = $i; $j < $levels; $j++) echo " ";
Bottom indentfor ($j = $levels; $j > $i; $j--) echo " ";
Digitsfor ($k = 1; $k < $i * 2; $k++) echo $k;

Printing Numbers vs Starting a New Line

APIEffectUse for
echo " " / echo $kStays on the same lineEach space or digit
echo PHP_EOLEnds the current lineAfter spaces and digits on a row

Print spaces and digits without a newline, then end the row once.

Try it

Live Preview

Change the level count and the number diamond updates instantly.

Whole numbers from 1 to 5 (peak stays within single digits 1–9). Tap a chip or type a value — the preview redraws as you go.

Live result 5 levels · 9 lines
    1
   123
  12345
 1234567
123456789
 1234567
  12345
   123
    1
Trace

Worked Walkthrough — $levels = 3

Trace spaces and digits on the way up, then back down.

Half$iSpaces / digitsPrinted row
Top12 / 11
Top21 / 123123
Top30 / 1234512345
Bottom21 / 123123
Bottom12 / 11

Total lines = 2 * $levels - 1. Digit count on row $i = 2 * $i - 1.

Code

PHP Programs

Three complete programs: fixed 5 levels, CLI input levels, and a compact 3-level demo. Use View Output for sample results.

Example 1 — Fixed $levels = 5

Top half grows to 123456789; bottom half mirrors back to 1.

PHP
<?php
for ($i = 1; $i <= 5; $i++) {
    for ($j = $i; $j < 5; $j++)
        echo " ";

    for ($k = 1; $k < $i * 2; $k++)
        echo $k;

    echo PHP_EOL;
}

for ($i = 4; $i >= 1; $i--) {
    for ($j = 5; $j > $i; $j--)
        echo " ";

    for ($k = 1; $k < $i * 2; $k++)
        echo $k;

    echo PHP_EOL;
}

How It Works

1. Top half. $i runs 1..5; print 5 - $i spaces, then digits while $k < $i * 2.

2. Bottom half. $i runs 4..1 with the same digit rule so the shape mirrors.

3. Peak. When $i = 5, digits are 1 through 9 — the widest row.

Example 2 — User Input (levels)

Read the level count from STDIN and build both halves from that value.

PHP
<?php
echo "Enter levels: ";
$input = trim(fgets(STDIN));

if (!is_numeric($input) || (int) $input < 1) {
    echo "Please enter a positive whole number." . PHP_EOL;
    exit(1);
}

$levels = (int) $input;

for ($i = 1; $i <= $levels; $i++) {
    for ($j = $i; $j < $levels; $j++)
        echo " ";

    for ($k = 1; $k < $i * 2; $k++)
        echo $k;

    echo PHP_EOL;
}

for ($i = $levels - 1; $i >= 1; $i--) {
    for ($j = $levels; $j > $i; $j--)
        echo " ";

    for ($k = 1; $k < $i * 2; $k++)
        echo $k;

    echo PHP_EOL;
}

How It Works

1. Validate levels. Check is_numeric; require $levels >= 1.

2. Same diamond. Both outer loops and space bounds use $levels instead of the literal 5.

Example 3 — Compact $levels = 3

A smaller fixed demo — easier to trace by hand before scaling up.

PHP
<?php
$levels = 3;

for ($i = 1; $i <= $levels; $i++) {
    for ($j = $i; $j < $levels; $j++)
        echo " ";

    for ($k = 1; $k < $i * 2; $k++)
        echo $k;

    echo PHP_EOL;
}

for ($i = $levels - 1; $i >= 1; $i--) {
    for ($j = $levels; $j > $i; $j--)
        echo " ";

    for ($k = 1; $k < $i * 2; $k++)
        echo $k;

    echo PHP_EOL;
}

How It Works

1. Same rules. Grow, then shrink; spaces then digits on every row.

2. Quick check. Five lines total; the middle row is 12345.

Edge Cases & Pitfalls

Check these before calling the solution done.

peak twice

Bottom loop starts at $levels

The widest row prints twice. Start the bottom at $levels - 1.

no spaces

Forget the space loops

Rows left-align and the diamond shape disappears. Keep $levels - $i spaces.

$k <= $i

Print only to $i

Rows become 1, 12, 123… instead of odd lengths. Use $k < $i * 2 (or $k <= 2*$i - 1).

levels > 5

Digits past 9

echo $k prints 10, 11… and columns break. Cap at 5 for single-digit rows, or format with fixed width.

levels = 1

Single cell

Output is just 1 — bottom loop never runs.

Bad input

(int) alone is not enough

Prefer is_numeric after trim(fgets(STDIN)) so non-numeric input does not silently become 0.

Analysis

Time and Space Complexity

ProgramTimeExtra space
Fixed / compact (Examples 1, 3)O(n²)O(1)
User input (Example 2)O(n²)O(1)

There are 2n - 1 rows and up to O(n) digits per row, so total work is quadratic in the level count.

Remember

Key Takeaways

  • Rule: grow $i to $levels, then shrink; each row prints 1..(2*$i-1).
  • Center: print $levels - $i spaces before the digits on every row.
  • echo vs PHP_EOL: spaces and digits stay on the line; echo PHP_EOL advances after each row.
  • Next step: Program 45 prints an X of stars and zeros on a grid.

One line: indent, print an odd-length ascending digit row, grow to the peak, then mirror down.

Frequently Asked Questions

A centered diamond of ascending digits: 1, 123, 12345, 1234567, 123456789, then the same rows mirrored back down to 1.
The row prints 2*$i-1 digits (odd length): 1, 3, 5, 7, 9, … using for ($k = 1; $k < $i*2; $k++).
A space loop prints leading spaces before the digits. Top half uses for ($j = $i; $j < $levels; $j++); bottom half uses for ($j = $levels; $j > $i; $j--).
The first builds the top half ($i = 1..$levels). The second mirrors back down ($i = $levels-1..1) to complete the diamond.
Program 43 is a right-aligned triangle with fixed-width columns. Program 44 is a symmetric centered diamond with odd-length digit rows.
Replace 5 with a $levels variable in both outer loops and space bounds — see Example 2.
O(n²) for n levels because each level prints O(n) digits and there are O(n) rows overall.
Use trim(fgets(STDIN)) and check is_numeric($input) before casting to int — see Example 2.
Only one row prints — a single centered 1.

Did you know?

Top half runs $i = 1..$levels; bottom half mirrors $i = $levels-1..1. Each row prints 2*$i-1 digits (1 to 2*$i-1) with leading spaces to center the diamond.

Next: X Pattern with Stars and Zeros

Print * on diagonals and the center column, 0 elsewhere.

Program 45 tutorial →

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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PHP Number Pattern 43 — Right-Aligned Number Triangle PHP Number Pattern 45 — X Pattern with Stars and Zeros