0-Centered Descending Mirror Number Pattern in PHP

What You’ll Learn

The 0-centered descending mirror pattern prints 0, 909, 89098, … up to 1234567890987654321 — a natural step after the palindrome triangle in Program 27. This tutorial covers three nested loops, a fixed zero center, a live preview, algorithm steps, worked PHP examples, edge cases, and complexity.

📝 Problem & Approach

Given max digit 9, print 10 rows of a 0-centered mirror: for each descending i, print i..9, then 0, then 9..i on the same line.

// max = 9 (conceptual shape)
// 0
// 909
// 89098
// 7890987
// ...
// 1234567890987654321

Inputs & Outputs

Minimal workflow

for i from max+1 down to 1:
    for j from i to max:
        print j
    print 0
    for k from max down to i:
        print k
    print newline

Approach comparison

🔮 Live Preview

Choose a max digit between 3 and 9 and draw the 0-centered mirror pattern in the browser.

Press "Draw pattern".

Examples Gallery

Three complete PHP programs — fixed max digit, custom max input, and spaced output variant. Click View Output to reveal sample console results.

<?php
for ($i = 10; $i >= 1; $i--) {
    for ($j = $i; $j < 10; $j++) {
        echo $j;
    }

    echo "0";

    for ($k = 9; $k >= $i; $k--) {
        echo $k;
    }

    echo PHP_EOL;
}

0
909
89098
7890987
678909876
56789098765
4567890987654
345678909876543
23456789098765432
1234567890987654321

<?php
echo "Enter max digit (1-9): ";
$max = (int) trim(fgets(STDIN));
if ($max < 1) $max = 1;
if ($max > 9) $max = 9;

for ($i = $max + 1; $i >= 1; $i--) {
    for ($j = $i; $j <= $max; $j++) {
        echo $j;
    }

    echo "0";

    for ($k = $max; $k >= $i; $k--) {
        echo $k;
    }

    echo PHP_EOL;
}

Enter max digit (1-9): 4
0
404
34043
2340432
123404321

<?php
$max = 9;

for ($i = $max + 1; $i >= 1; $i--) {
    for ($j = $i; $j <= $max; $j++) {
        echo $j . " ";
    }

    echo "0 ";

    for ($k = $max; $k >= $i; $k--) {
        echo $k . " ";
    }

    echo PHP_EOL;
}

0 
9 0 9 
8 9 0 9 8 
7 8 9 0 9 8 7 

🔎 Worked Walkthrough — max = 9 (selected rows)

Trace selected outer-loop values of i, the left half, center, right half, and full row output.

When i = max + 1, both inner loops are empty — only 0 prints. Each row grows as i decreases.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices