A rotating alphabet pattern reprints the same letter set each row, starting one letter further along and wrapping earlier letters in reverse so every line stays the same length.
Remember
Rule: for start i, print i..top, then reverse wrap of A..(i-1)
ABCDE
BCDEA
CDEBA
DECBA
EDCBA ← top = 'E' (5 letters each row)
Not a pure left rotation: after BCDEA you get CDEBA (reverse wrap), not CDEAB. Print $k - 1 on the wrap loop so the row-start letter is not duplicated.
Approach
How to Solve It
Two ways to emit the same rows — nested index/char loops, then optionally a suffix + reverse-prefix rewrite.
Method
Idea
Best for
Forward + wrap
Print $i..$top, then wrap with $k - 1
Learning, interviews, exams
String slice
Suffix from $i + reverse of prefix
Readable rewrite once the idea clicks
Pseudocode
Pseudocode
for $i from 'A' to $top:
for $j from $i to $top:
echo $j
for $k from $i down to 'B':
echo ($k - 1)
echo PHP_EOL
Cheat sheet
Goal
Pattern
Letter table
$alpha = str_split("ABCDEFGHIJKLMNOPQRSTUVWXYZ");
Row starts
for ($i = 0; $i <= 4; $i++) (A..E)
Forward run
for ($j = $i; $j <= 4; $j++) echo $alpha[$j];
Reverse wrap
for ($k = $i; $k > 0; $k--) echo $alpha[$k - 1];
End the row
echo PHP_EOL;
Row length
ord($top) - ord('A') + 1 (same on every row)
Avoid double start
Print $k - 1, not $k, on the wrap loop
Printing Letters vs Starting a New Line
API
Effect
Use for
echo
Stays on the same line
Each letter on forward and wrap
echo PHP_EOL
Ends the current line
After both inner loops
Print characters without a newline, then end the row once.
Try it
Live Preview
Change the top letter and the rotating rows update instantly — every line stays the same length.
One letter from A to F. Tap a chip or type a letter — the preview redraws as you go.
Live resultTop E · 5 rows · 5 letters/row
ABCDE
BCDEA
CDEBA
DECBA
EDCBA
Trace
Worked Walkthrough — A–E
Trace each row’s forward run, reverse wrap, and full line.
$i
Forward
Wrap (rev)
Printed row
0 (A)
ABCDE
(empty)
ABCDE
1 (B)
BCDE
A
BCDEA
2 (C)
CDE
BA
CDEBA
3 (D)
DE
CBA
DECBA
4 (E)
E
DCBA
EDCBA
Every row length is 5. Note the wrap is the reverse of the prefix — row 3 is CDEBA, not CDEAB.
Code
PHP Programs
Three complete programs: fixed A–E, top-letter input, and a string-slice rewrite. Use View Output to reveal sample results.
1. Slice the suffix.substr($letters, $i) is the forward run from the start index.
2. Reverse the prefix. Letters before $i are reversed with strrev and appended — same wrap as Examples 1–2.
3. One echo. Concatenate and print the full row in a single call.
For $i = 2, forward is CDE and reversed prefix is BA → CDEBA.
Edge Cases & Pitfalls
Check these before calling the solution done.
Print $k
Duplicate start letter
If the wrap loop prints $k instead of $k - 1, rows like BCDE B repeat the start. Always use $k - 1.
Forward wrap
Pure left rotation
Appending the prefix in order gives CDEAB, not CDEBA. This pattern reverses the wrap.
PHP_EOL inside
Column of letters
If echo PHP_EOL is inside either inner loop, each letter lands on its own line. Use echo for letters; end the row only after both loops.
$top = A
Single letter
Output is just A — wrap never runs. A good sanity check.
$top < A
Empty output
Outer loop never runs if $top < 'A'. Validate A–Z before looping.
Bad input
Validate one letter
Trim, uppercase, and require length 1 in A–Z — reject empty or multi-character tokens.
Analysis
Time and Space Complexity
Program
Time
Extra space
Forward + wrap (Examples 1–2)
O(n²)
O(1) (plus the fixed alphabet table)
String slice (Example 3)
O(n²)
O(n) per temporary row string
For $n = ord($top) - ord('A') + 1 letters, each of $n rows prints $n characters — still quadratic in $n.
Remember
Key Takeaways
Rule: for start $i, print $i..$top, then reverse wrap of A..(i-1).
No duplicate start: wrap with $k - 1, not $k.
Break the row: call echo PHP_EOL only after both loops.
Complexity:O(n²) time; O(1) extra space for nested loops.
One line: for each start $i, echo $i..$top, then the reverse of A..(i-1), then echo PHP_EOL.
Frequently Asked Questions
The first loop prints from the row start through E (or your top letter). The second prints the letters before the start (wrapping) in reverse using k-1 so the boundary letter is not duplicated.
When k equals i, printing k would repeat the first letter of the row. Printing k-1 starts the wrap with the previous letter (e.g. BCDE then A gives BCDEA).
Each row prints from the row start to the end, then prints earlier letters in reverse to complete the row. That creates the rotation effect.
Yes. Forward length plus wrap length equals ord('E')-ord('A')+1, so each row has the same number of letters.
Not exactly. A pure left rotation of ABCDE would give BCDEA, CDEAB, DEABC, EABCD. This pattern wraps earlier letters in reverse, so you get CDEBA, DECBA, EDCBA.
echo stays on the same line. echo PHP_EOL ends the current line. Letters use echo; the row break uses echo PHP_EOL after both inner loops.
For n letters, each of n rows prints n characters, so O(n²).
Use trim(fgets(STDIN)), take the first character after strtoupper, require A–Z, and reject empty or multi-character tokens.
🤔
Did you know?
Outer i is the row start. First inner loop prints i through E. Second inner loop wraps by counting down from i and printing k - 1 (not k) so the boundary letter isn’t duplicated. Every row prints the same length: ord('E') - ord('A') + 1 letters.
