1. Same continuous stream.$k still starts at 'A' outside the outer loop.
2. Name the width.$count = $n - $i + 1 makes the shrink rule obvious — row 1 prints 5 letters; row 5 prints 1.
3. Simple spacing.$k++ . " " skips width-2 formatting and adds a plain space after each letter.
Edge Cases & Pitfalls
Check these before calling the solution done.
Reset $k
Every row starts at A
If you put $k = 'A' inside the outer loop, you lose the continuous stream. Keep $k outside.
$j = 1..$i
Growing triangle by mistake
An ascending inner bound reprints a growing shape. Use $j from $n down to $i (or $count = $n - $i + 1).
PHP_EOL inside
Column of letters
If echo PHP_EOL is inside the inner loop, each letter lands on its own line. Use echo/printf for letters; end the row only after the inner loop.
$n = 1
Single A
Output is just A. A good sanity check.
Past Z
Letter budget
Total letters = n(n+1)/2. For A–Z only, keep that ≤ 26 (so $n ≤ 6 without wrapping).
Bad input
Use is_numeric
Casting non-numeric input to int becomes 0. Prefer is_numeric and require $n ≥ 1.
Analysis
Time and Space Complexity
Program
Time
Extra space
Countdown inner (Examples 1–2)
O(n²)
O(1)
Explicit count (Example 3)
O(n²)
O(1)
Total letters = n + (n - 1) + … + 1 = n(n + 1)/2 — still quadratic in $n. Same totals as an inverted triangle of stars; only the printed symbols differ.
Remember
Key Takeaways
Rule: keep $k outside; row $i prints $n - $i + 1 letters from $k++.
Never reset: putting $k = 'A' inside the outer loop restarts every row.
Break the row: call echo PHP_EOL only after the inner loop.
Complexity:O(n²) time from the triangular letter count; O(1) extra space.
One line: for each row $i, echo $n - $i + 1 letters from the shared $k++ stream, then call echo PHP_EOL.
Frequently Asked Questions
Because the pattern is one continuous alphabet stream A through O. Resetting k would restart each row from A.
So the sequence continues across rows (A, B, C, ...). If you reset k each row, every row would start at A again.
For the fixed 5-row example, the row lengths are 5, 4, 3, 2, 1. Each new row prints one fewer letter.
The width-2 formatting aligns the columns (best in a monospace terminal). Adding a trailing space makes the output match the sample with spaces between letters.
Build a row string and trim it, or print a space only between letters (not after the last letter in the row).
Both use a continuous k++ stream. Program 22 grows rows and right-aligns with pad cells; this pattern shrinks row length each time and stays left-aligned.
O(n²) for n rows because total prints are 1+2+...+n = n(n+1)/2.
Use trim(fgets(STDIN)) and check is_numeric($input) before casting to int, require n ≥ 1, and cap so n(n+1)/2 ≤ 26 if you want only A–Z letters.
🤔
Did you know?
One counter k starts at A and never resets. The outer loop controls row count; the inner loop length decreases each row (5, 4, 3, 2, 1). Width-2 formatting (or a trailing space) keeps a clean column layout in monospace output.
