Symmetric Alphabet Pyramid in PHP

What You’ll Learn

Print centered palindromic rows — A, ABA, ABCBA, up to ABCDEDCBA — by padding with spaces, climbing A..i, then mirroring (i-1)..A without repeating the middle letter. Compare Program 18 and Program 24 for related palindrome pyramids. Includes a live preview, worked PHP examples, edge cases, and complexity.

📝 Problem & Approach

Given a top letter (or fixed E), print a centered pyramid of alphabet palindromes ending at that letter.

// Five rows (top = E)
//     A
//    ABA
//   ABCBA
//  ABCDCBA
// ABCDEDCBA

Inputs & Outputs

Minimal workflow

$end = ord($top) - ord('A')
for i from 0 to end:
    print (end - i) spaces
    for k from 0 to i:                 // ascending A..i
        print letter[k]
    $n = $k - 1                          // peak index
    repeat i times:
        print letter[--$n]              // (i-1)..A
    print newline

Approach comparison

🔮 Live Preview

Choose a top letter from A to F and draw the symmetric alphabet pyramid in the browser.

Press "Draw pattern".

Examples Gallery

Three complete PHP programs — fixed A–E, user-chosen top letter, and an explicit-mirror rewrite. Click View Output to reveal sample console results.

<?php
$alpha = str_split("ABCDEFGHIJKLMNOPQRSTUVWXYZ");

for ($i = 0; $i <= 4; $i++) {
    for ($j = 4; $j > $i; $j--)
        echo " ";

    for ($k = 0; $k <= $i; $k++)
        echo $alpha[$k];

    $n = $k - 1;
    for ($m = 0; $m < $i; $m++)
        echo $alpha[--$n];

    echo PHP_EOL;
}

    A
   ABA
  ABCBA
 ABCDCBA
ABCDEDCBA

<?php
echo "Enter top letter (like E): ";
$top = strtoupper(trim(fgets(STDIN)))[0];

$end = ord($top) - ord('A');
$alpha = str_split("ABCDEFGHIJKLMNOPQRSTUVWXYZ");

for ($i = 0; $i <= $end; $i++) {
    for ($j = $end; $j > $i; $j--)
        echo " ";

    for ($k = 0; $k <= $i; $k++)
        echo $alpha[$k];

    $n = $k - 1;
    for ($m = 0; $m < $i; $m++)
        echo $alpha[--$n];

    echo PHP_EOL;
}

Enter top letter (like E): C
  A
 ABA
ABCBA

<?php
$end = 4;
$alpha = str_split("ABCDEFGHIJKLMNOPQRSTUVWXYZ");

for ($i = 0; $i <= $end; $i++) {
    for ($j = $end; $j > $i; $j--)
        echo " ";

    for ($k = 0; $k <= $i; $k++)
        echo $alpha[$k];

    for ($p = $i - 1; $p >= 0; $p--)
        echo $alpha[$p];

    echo PHP_EOL;
}

    A
   ABA
  ABCBA
 ABCDCBA
ABCDEDCBA

🔎 Worked Walkthrough — Top = E (end = 4)

Trace padding, ascending half, and mirrored descending half for each row.

After ascending, k = i + 1, so $n = $k - 1 = i. The first --$n lands on i - 1.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

For n rows each row prints O(n) spaces and letters combined, so total work is O(n²).

💡 Best Practices