A reverse repeating alphabet triangle grows by one repeated letter on each new line while letters count downward from the top of the alphabet range.
Remember
Rule: for letter i from top down to 'A',
print i with growing width 1, 2, 3, …
E
DD
CCC
BBBB
AAAAA ← 5 rows (top = 'E')
It is the reverse of Program 9: same growing widths, but letters step E → A instead of A → E. Print the outer letter inside the inner loop so each row stays uniform. Flip the widths in Program 11 to get the inverted twin.
Approach
How to Solve It
Two ways to emit the same shape — start with nested ord/chr loops, then optionally shorten with string multiplication.
Method
Idea
Best for
Nested loops
Outer = letter; inner = growing width; print outer letter
Learning, interviews, exams
ch * repeat
Build a whole repeated-letter row in one call
Shorter demos once loops click
Pseudocode
Pseudocode
for i from top down to 'A':
for j from top down to i:
print i (no newline)
print newline
Print letters without a newline, then end the row once.
Try it
Live Preview
Change the height and the reverse repeating triangle updates instantly — including the letter total.
Whole numbers from 1 to 26 (A–Z). Tap a chip or type a value — the preview redraws as you go.
Live result5 rows · 15 letters
E
DD
CCC
BBBB
AAAAA
Trace
Worked Walkthrough — 'E' down to 'A'
Trace each outer-loop value of i and count how many times the inner loop runs.
i
Inner j range
Printed row
Repeats
'E'
'E'..'E'
E
1
'D'
'E'..'D'
DD
2
'C'
'E'..'C'
CCC
3
'B'
'E'..'B'
BBBB
4
'A'
'E'..'A'
AAAAA
5
Total letter prints: 1 + 2 + 3 + 4 + 5 = 15 = 5×6/2. That triangular sum is why time is O(n²).
Code
Python Programs
Three complete programs: fixed letters, input(), and a ch * repeat shortcut. Use View Output to reveal sample results.
Example 1 — Fixed 'E' down to 'A'
Hard-coded range — outer letter counts down; inner loop grows and prints that letter.
Python
top = ord('E')
for i in range(top, ord('A') - 1, -1):
for j in range(top, i - 1, -1):
print(chr(i), end="")
print()
Output
E
DD
CCC
BBBB
AAAAA
How It Works
1. Outer loop picks the letter.i runs from ord('E') down to ord('A').
2. Inner loop sets the width.j runs from top down to i — once for E, twice for D, and so on.
3. Print the outer letter.print(chr(i), end="") keeps the whole row the same character.
4. Break the line. Bare print() after the inner loop starts the next row.
Example 2 — User Input Version
Compute top = ord('A') + rows - 1, then grow repeat from 1 as letters count down. Prefer try/except ValueError in real apps.
Python
raw = input("Enter the number of rows: ").strip()
try:
rows = int(raw)
except ValueError:
print("Please enter a whole number of rows >= 1.")
else:
if rows < 1:
print("Please enter a whole number of rows >= 1.")
else:
if rows > 26:
rows = 26
top = ord('A') + rows - 1
repeat = 1
for code in range(top, ord('A') - 1, -1):
ch = chr(code)
for k in range(repeat):
print(ch, end="")
print()
repeat += 1
Output (when user enters 4)
Enter the number of rows: 4
D
CC
BBB
AAAA
How It Works
1. Prompt and parse. Ask for a row count, then convert with int(...) inside try/except ValueError.
2. Compute the top letter. For rows = 4, top is ord('D') — first row is D.
3. Grow the repeat count. Start at repeat = 1 and increment after each row so widths become 1, 2, 3, 4.
4. Clamp for A–Z. Cap at 26 so codes stay in the alphabet for demos.
Example 3 — ch * repeat
Build each repeated-letter row in one call — same shape, no explicit character loop.
Python
rows = 5
top = ord('A') + rows - 1
repeat = 1
for code in range(top, ord('A') - 1, -1):
print(chr(code) * repeat)
repeat += 1
Output
E
DD
CCC
BBBB
AAAAA
How It Works
1. Same countdown. Still walk code from top down to ord('A').
2. Build the row.chr(code) * repeat creates a string of length repeat filled with that letter.
3. Learn loops first. Use Examples 1–2 when you need to show nested bounds; treat this as a polish shortcut afterward.
Edge Cases & Pitfalls
Check these before calling the solution done.
print(j)
Stepping letters on a row
If you print chr(j) instead of chr(i), letters change across the row. Print the outer letter to keep each row uniform.
step +1
Forward triangle by mistake
Counting letters upward reprints Program 9. Keep range(..., -1) from the top letter down to 'A'.
print early
Column of letters
If bare print() (or default print(chr(i))) is inside the inner loop, each letter lands on its own line. Use end="" for letters; call print() only after the inner loop.
rows > 26
Past Z
ord('A') + rows - 1 leaves A–Z when rows > 26. Clamp or reject in interactive programs.
rows = 1
Single A
Output is just A — top and tip coincide. A good sanity check.
Bad input
Catch ValueError
Bare int(input()) raises on letters — wrap in try/except ValueError and require 1–26.
Analysis
Time and Space Complexity
Program
Time
Extra space
Nested loops (Examples 1–2)
O(rows²)
O(1)
ch * repeat (Example 3)
O(rows²)
O(rows) per temporary row string
Total letters = 1 + 2 + … + n = n(n + 1)/2 — still quadratic in n. Same totals as Program 11; only the print order of widths differs.
Remember
Key Takeaways
Rule: countdown letter i; print i with growing width 1, 2, 3, …
Reverse of Program 9: same growing widths — letters step down instead of up.
Break the row: call bare print() only after the inner loop.
Complexity:O(n²) time from the triangular letter count; O(1) extra space for nested loops.
One line: for i from the top letter down to 'A', print i for every j from top down to i, then print().
Frequently Asked Questions
Program 9 uses A, BB, CCC, ... (letters increase). Program 10 uses E, DD, CCC, ... (letters decrease) with the same growing repeat counts.
On the 4th row the outer-loop letter is B, and the inner loop runs four times, printing B each time.
The inner loop only controls how many times to print. Printing the outer letter keeps the row uniform; printing the inner counter would change letters across the row.
With for j in range(top, i - 1, -1), when i is near the top the range is short; as i moves toward A the range lengthens, so repeat counts grow 1, 2, 3, …
print(ch, end="") stays on the same line. print() ends the current line. Letters use end=""; the row break uses print() after the inner loop.
O(n²) where n is the number of rows. Total printed characters equal 1+2+…+n = n(n+1)/2.
Yes. print(ch * repeat) prints a full repeated-letter row in one call. Nested loops are better for learning; ch * repeat is a handy shortcut later.
Use a try/except ValueError around int(input()), or check raw.isdigit() before converting, then clamp rows between 1 and 26 so bad input does not walk past A.
🤔
Did you know?
This pattern is the reverse of Program 9: row widths still grow 1, 2, 3, …, but letters run backward (E, then D, then C, …). Print the outer loop letter inside the inner loop so each row stays uniform.
