Inverted Repeating-Letter Alphabet Triangle in JavaScript

Beginner

⏱️ 8 min read

📚 Updated: Aug 2026

🎯 3 Code Examples

🚀 Live Preview

Nested Loops

Inverted repeating triangle EEEEE, DDDD, CCC, BB, A in JavaScript programming

Overview

What You’ll Learn

First row: five Es. Each following row is one character shorter and uses the next letter down: EEEEE, DDDD, CCC, BB, A. Compare with Program 10 (width grows) and worked JavaScript examples, live preview, edge cases, and complexity.

Shape Rule

Wide first, then shrink

Row 1 prints EEEEE, then DDDD, down to a single A.

Outer Loop

Letter countdown

for (let i = "E".charCodeAt(0); i >= "A".charCodeAt(0); i--) picks the letter for each row.

Inner Loop

Width 5…1

for (let j = "A".charCodeAt(0); j <= i; j++) shrinks as i falls - print String.fromCharCode(i), not the inner counter.

line vs console.log

Same line / next line

Letters use line += ch; end each row with console.log(line).

Live Preview

1–26 rows

Pick a row count and draw the inverted repeating triangle in the browser.

O(n²)

Complexity

Total letters = n(n+1)/2; extra memory stays O(1).

Introduction

An inverted repeating alphabet triangle starts wide and shrinks by one repeated letter on each new line, counting letters downward from the top of the alphabet range. With the right angle on the left, the console shows an upside-down staircase of identical letters per row.

In JavaScript you usually solve it with two nested for loops: the outer loop picks the row letter (counting down), the inner loop prints that same letter fewer times each row, then console.log(line) moves to the next line.

Why it matters?

It shows that “inverted” often means flipping only the width bound - not inventing a new algorithm. Once outer letter vs inner count clicks, Program 10, 11, and 12 are one-line cousins.

Key Highlights

Widest First

Top row repeats the highest letter n times.

Width Shrinks

Rows go 5, 4, 3, …, 1 while letters go E→A.

Print Outer Letter

line += String.fromCharCode(i) in the inner loop; console.log(line) after.

Invert of Program 10

Same letters - opposite width direction.

In short: for each letter i from top down to A, print i repeatedly (i - "A".charCodeAt(0) + 1) times, then call console.log(line).

Foundation

📝 Problem & Approach

Given a positive integer rows (or a fixed top letter like 'E'), print a left-aligned inverted triangle where each row repeats one letter and widths shrink from rows down to 1.

JavaScript

// First 5 rows (conceptual shape)
// EEEEE
// DDDD
// CCC
// BB
// A

Inputs & Outputs

Item	Type	Description
`rows`	int	Number of triangle lines (typically 1–26). Top letter = `String.fromCharCode("A".charCodeAt(0) + rows - 1)`.
Printed output	text	Left-aligned rows; letter `ch` is repeated `code - base + 1` times.

Minimal workflow

Pseudocode

top = "A".charCodeAt(0) + rows - 1
for code from top down to "A".charCodeAt(0):
    repeat = code - "A".charCodeAt(0) + 1
    for k from 1 to repeat:
        print String.fromCharCode(code) (no newline)
    console.log the row

Approach comparison

Approach	Idea	Best for
Nested char loops	Outer letter + inner `A..i` width	Learning and interviews
`ch.repeat(repeat)`	Build a whole row in one call	Shorter production-style demos

Cheat Sheet

⚡ Quick Reference

Goal	Pattern
Walk letters downward	`for (let i = "E".charCodeAt(0); i >= "A".charCodeAt(0); i--)`
Shrink repeat count	`for (let j = "A".charCodeAt(0); j <= i; j++)`
Print row letter	`line += String.fromCharCode(i)` — not the inner counter
End the row	`console.log(line)`
One-line row shortcut	`console.log(ch.repeat(repeat))`
Growing widths	See Program 10 (E, DD, CCC, …)

Compare

📋 line vs console.log vs *

Same triangle - different ways to emit characters.

line += ch

same line

Prints a letter without moving to the next line

console.log(line)

new line

Ends the current row after all repeats are printed

ch * n

whole row

Builds n copies of ch at once - skip the inner loop

Learning tip

print String.fromCharCode(i)

Master printing the outer letter before the string shortcut

Context

When This Pattern Shows Up

Reach for this triangle when practicing inverted widths with repeating letters.

After Program 10
Flip only the width direction while keeping letter countdown.
Bound-flip drills
j <= i from A naturally shrinks as i falls.
Char arithmetic practice
Use repeat = code - base + 1 instead of a growing formula.
Gateway to Program 12
Next: same shrink, but letters advance A→E.
Not a UI layout tool
This is a console teaching pattern - not how you build modern app screens.

Key benefit: one small program that proves inversion is usually a bound change - letter choice and width can flip independently.

Interactive

🔮 Live Preview

Choose a row count between 1 and 26 and draw the inverted repeating alphabet triangle in the browser.

Hands-On

Examples Gallery

Three complete JavaScript programs - fixed E-to-A range, prompt input, and a ch.repeat(repeat) shortcut. Click View Output to reveal sample console results, or Try it Yourself to run in the browser editor.

📚 Getting Started

Print five shrinking rows with classic nested char loops.

Example 1 — Fixed `'E'` down to `'A'`

Hard-coded range - ideal for first demos and screenshots.

JavaScript

const top = "E".charCodeAt(0);
const base = "A".charCodeAt(0);

for (let i = top; i >= base; i--) {
  const ch = String.fromCharCode(i);
  let line = "";
  for (let j = base; j <= i; j++) {
    line += ch;
  }
  console.log(line);
}

Try it Yourself

How It Works

When i is "E".charCodeAt(0), the inner loop runs from A to E (5 times) and builds EEEEE. When i is "D".charCodeAt(0), it builds DDDD, and so on until a single A. Appending ch from the outer letter (not the inner counter) keeps each row uniform.

📈 Practical Variant

Let the user choose the height at runtime.

Example 2 — User Input Version

Compute top = "A".charCodeAt(0) + rows - 1, then shrink with repeat = code - base + 1. Validate parseInt(prompt()) with Number.isFinite in real apps.

JavaScript

const rowsInput = prompt("Enter the number of rows:");
let rows = parseInt(rowsInput, 10);
rows = Math.max(1, Math.min(rows, 26));

const base = "A".charCodeAt(0);
const top = base + rows - 1;

for (let code = top; code >= base; code--) {
  const ch = String.fromCharCode(code);
  const repeat = code - base + 1;
  let line = "";
  for (let k = 0; k < repeat; k++) {
    line += ch;
  }
  console.log(line);
}

Try it Yourself

How It Works

For rows = 4, top is "D".charCodeAt(0). Letter D repeats 4 times, C three times, and so on. Clamp rows to 1-26 so top stays within A-Z.

⚡ Shortcut Style

Same shape without an explicit inner append loop.

Example 3 — `ch.repeat(repeat)`

Build each repeated-letter row in one call, then log it.

JavaScript

const rows = 5;
const base = "A".charCodeAt(0);
const top = base + rows - 1;

for (let code = top; code >= base; code--) {
  const ch = String.fromCharCode(code);
  const repeat = code - base + 1;
  console.log(ch.repeat(repeat));
}

Try it Yourself

How It Works

ch.repeat(repeat) creates a string of length repeat filled with that letter. Great once you understand the nested-loop idea; keep the two-loop version for exams that ask you to show both bounds.

🧠 How the Algorithm Prints Rows

Set up

Use prompt() when reading input. Fix the top letter or compute it from rows.

Setup

Outer loop (letter)

for (let i = "E".charCodeAt(0); i >= "A".charCodeAt(0); i--) selects the character printed on the row.

E → A

Inner loop (width)

for (let j = "A".charCodeAt(0); j <= i; j++) runs 5, 4, 3… times; print String.fromCharCode(i) with line += String.fromCharCode(i).

5..1

New line

console.log(line) ends the row so the next outer iteration starts fresh.

Break

Triangle complete

Total letters: n+(n-1)+…+1 = n(n+1)/2 — O(n²) time, O(1) extra memory.

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'`	`'A'..'E'`	`EEEEE`	5
`'D'`	`'A'..'D'`	`DDDD`	4
`'C'`	`'A'..'C'`	`CCC`	3
`'B'`	`'A'..'B'`	`BB`	2
`'A'`	`'A'..'A'`	`A`	1

Total letter prints: 5 + 4 + 3 + 2 + 1 = 15 = 5×6/2.

Use Cases

Where this tiny pattern (and its loop structure) shows up beyond the homework prompt.

1. Bound Flip Practice

Clearest demo that j <= i from A shrinks as i falls.

Example: compare with Program 10’s growing inner bound.

2. Pair with Program 10

Teach grow vs shrink as a one-bound change.

Example: side-by-side E/DD/CCC vs EEEEE/DDDD/CCC.

3. Char Math Labs

Practice code - base + 1 for shrinking widths.

Example: "D".charCodeAt(0) - "A".charCodeAt(0) + 1 = 4.

4. Case & Fill Variants

Swap to lowercase or mix digits once the loops work.

Example: start from String.fromCharCode("a".charCodeAt(0) + rows - 1).

5. Complexity Intuition

Descending triangular totals still make O(n²) concrete.

Example: 5+4+…+1 = 15 for n = 5.

6. Input Validation Labs

Pair the pattern with Number.isFinite and 1–26 clamps.

Example: reject rows <= 0 or rows > 26.

Pro Tip: say “outer picks the letter, inner shrinks the width” before coding - that story prevents mixing Program 10’s growing formula here.

Advantages

Why this pattern earns a spot right after the growing reverse triangle.

1. Instant Visual Feedback
Wrong width formula shows up immediately as a growing instead of shrinking shape.
2. Minimal Concepts
Only loops, chars, and console output - no arrays required.
3. Easy to Mirror
Flip to Program 10 by growing the repeat count instead.
4. O(1) Extra Memory
Streaming output needs no storage beyond loop counters.

Pro Tip: learn the nested-loop version first; treat ch.repeat(repeat) as a polish shortcut afterward.

Usage Tips

Small habits that keep alphabet-pattern code clean.

1. Name the Roles
Use ch for the row letter and repeat = code - base + 1 for the shrinking count.
2. Validate prompt() input
Avoid crashes when the user types letters instead of a number.
3. Keep console.log(line) Outside
Only call console.log(line) after the inner loop finishes the row.
4. Clamp to 26
For A–Z demos, reject or clamp rows > 26.
5. Dry-Run One Small n
Trace rows = 3 (CCC, BB, A) on paper before coding larger demos.

Pro Tip: if you get E, DD, CCC instead of EEEEE, DDDD, CCC, you reused Program 10’s growing repeat formula.

Common Pitfalls

Mistakes that commonly break inverted repeating alphabet patterns.

1. Printing j Instead of i
Rows become A…E sequences instead of repeated letters.
→ Always line += String.fromCharCode(i) (or ch) for this shape.
2. Using Program 10’s Growing Formula
repeat = (top - code) + 1 grows widths - wrong for this page.
→ Use repeat = code - base + 1 (or j from A to i).
3. console.log(line) Inside the Inner Loop
Each letter lands on its own line - you get a column, not a triangle.
→ Use line += ch for letters; console.log(line) only after the inner loop.
4. Blind parseInt(prompt())
Non-numeric input yields NaN with bare parseInt(prompt()).
→ Validate parseInt(prompt()) with Number.isFinite and validate range.
5. rows > 26 Without a Policy
String.fromCharCode("A".charCodeAt(0) + rows - 1) can leave the A–Z range.
→ Clamp to 26 or define wrap/error behavior explicitly.

Edge Cases

Check these inputs before calling the solution done.

rows = 1

Single letter

Output is just A on one line.

rows = 0

Empty pattern

Treat as invalid; re-prompt instead of silent empty output.

Negative

`rows < 0`

Invalid height - validate before computing top.

rows > 26

Past Z

Clamp or error - char math leaves A–Z.

Bad input

Non-numeric input

Non-numeric input becomes 0 - check Number.isFinite first.

Case

Lowercase variant

Same loops work with 'a' and String.fromCharCode("a".charCodeAt(0) + rows - 1).

Drill

🎯 Practice Problems

Try these variations to lock in the pattern.

1. Flip to Program 10

Grow widths: E, DD, CCC, …
Continue with Program 10

2. Forward letters (Program 12)

Keep shrinking widths, advance A→E
See Program 12

3. Safe input loop

Use Number.isFinite until 1 <= rows <= 26
Then draw the triangle

4. Lowercase version

Use String.fromCharCode("a".charCodeAt(0) + rows - 1) as the top letter
Shows the loop structure is reusable

Important

Notes

Triangular count. Total letters for n rows is still n(n+1)/2 - hence O(n²) time.
Print the outer letter; the inner loop only decides how many times (shrinking).
Validate 1 <= rows <= 26 for interactive A–Z programs.
This page is left-aligned. Centered pyramids need leading spaces - covered later in the series.

Quick Takeaway: outer loop picks the letter (counting down), inner loop shrinks the width, then break the line - that is the whole pattern.

Analysis

⏱️ Time and Space Complexity

Program	Time	Extra space
Nested loops (Examples 1-2)	`O(rows²)`	`O(1)`
`ch.repeat(repeat)` (Example 3)	`O(rows²)`	`O(rows)` per row string (temporary)

Wrap Up

🎉 Conclusion

The inverted repeating alphabet triangle is a small nested-loop exercise with lasting payoff: outer letter vs shrinking width, char countdown, and O(n²) intuition. Master the classic two-loop version, then optionally shorten rows with ch.repeat(repeat).

Practice the three examples above, then compare with Program 10 or continue to Program 12’s forward-letter invert.

Print the outer letter with line += ch, end rows with console.log(line), and use code - base + 1 (not Program 10’s growing formula) for the width.

View Examples Gallery Continue to Program 12

Pro Tips

💡 Best Practices

✅ Do

Explain outer = letter, inner = shrinking width before coding
Use line += String.fromCharCode(i) for letters and console.log(line) after each row
Validate 1 <= rows <= 26 for interactive programs
Check Number.isFinite after prompt()
State O(n²) time when asked about complexity

❌ Don’t

Print the inner-loop variable for this repeating shape
Reuse Program 10’s growing repeat formula here
Call console.log(line) inside the inner letter loop
Ignore bad console input in user-facing demos
Allow rows > 26 without a clear policy

Summary

Key Takeaways

Knowledge Unlocked

Five things to remember about this alphabet pattern

Print the inverted repeating triangle the beginner-friendly way.

Core concepts

▽ 01

Rule

Letters down, width down

Definition

↻ 02

Outer loop

Picks the row letter

Code

A 03

Inner loop

Shrinks with line += String.fromCharCode(i)

Code

↵ 04

console.log(line)

Ends each row

I/O

O 05

Complexity

O(n²) time

Analysis

❓ Frequently Asked Questions

How is this different from Program 10?

Program 10 prints widths 1..5 (E, DD, CCC, ...). Program 11 prints widths 5..1 (EEEEE, DDDD, ...). Both use repeating letters per row and letters counting down.

How does the program print EEEEE then DDDD?

When i is "E".charCodeAt(0), the inner loop runs from A through E (5 times) and appends E each time. Next i becomes "D".charCodeAt(0), the inner loop runs 4 times and appends D.

Why append the outer letter and not the inner counter?

The inner loop only controls how many times to append. Using the outer letter keeps the entire row the same letter; using the inner counter would step letters across the row.

Why does the width shrink as letters go down?

Because the inner loop runs from "A".charCodeAt(0) through i. Smaller i means fewer iterations, so fewer characters are appended.

What is the difference between building a line and logging inside the inner loop?

line += ch builds the full row string. console.log() inside the inner loop would log one letter per line. Log once after the inner loop finishes.

What is the time complexity?

O(n^2) where n is the number of rows. Total logged characters equal n+(n-1)+...+1 = n(n+1)/2.

Can I use String.repeat instead of an inner loop?

Yes. console.log(ch.repeat(repeat)) logs a full repeated-letter row in one call. Nested loops are better for learning; ch.repeat is a handy shortcut later.

How should I read the row count safely?

Use parseInt with Number.isFinite after prompt(), then clamp rows between 1 and 26 so the top letter stays within A-Z.

Did you Know? 🔊

This is the inverted twin of Program 10: letters still step E→A, but widths shrink 5, 4, 3, …, 1 instead of growing. Append the outer loop letter inside the inner loop so each row stays uniform.

Continue to Alphabet Pattern 12

Keep the shrinking widths, but advance letters forward: AAAAA, BBBB, CCC, …

Program 12 tutorial →

About the author

Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

Experience 12 years building web and cloud systems
Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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JavaScript Alphabet Pattern 10 - Reverse Repeating Triangle JavaScript Alphabet Pattern 12 - Inverted Forward Repeats

Inverted Repeating-Letter Alphabet Triangle in JavaScript

What You’ll Learn

Shape Rule

Outer Loop

Inner Loop

line vs console.log

Live Preview

O(n²)

Introduction

Why it matters?

Widest First

Width Shrinks

Print Outer Letter

Invert of Program 10

📝 Problem & Approach

Inputs & Outputs

Minimal workflow

Approach comparison

⚡ Quick Reference

📋 line vs console.log vs *

When This Pattern Shows Up

After Program 10

Bound-flip drills

Char arithmetic practice

Gateway to Program 12

Not a UI layout tool

🔮 Live Preview

Examples Gallery

📚 Getting Started

Example 1 — Fixed 'E' down to 'A'

How It Works

📈 Practical Variant

Example 2 — User Input Version

How It Works

⚡ Shortcut Style

Example 3 — ch.repeat(repeat)

How It Works

🧠 How the Algorithm Prints Rows

Set up

Outer loop (letter)

Inner loop (width)

New line

Triangle complete

🔎 Worked Walkthrough — 'E' down to 'A'

Use Cases

1. Bound Flip Practice

2. Pair with Program 10

3. Char Math Labs

4. Case & Fill Variants

5. Complexity Intuition

6. Input Validation Labs

Advantages

1. Instant Visual Feedback

2. Minimal Concepts

3. Easy to Mirror

4. O(1) Extra Memory

Usage Tips

1. Name the Roles

2. Validate prompt() input

3. Keep console.log(line) Outside

4. Clamp to 26

5. Dry-Run One Small n

Common Pitfalls

1. Printing j Instead of i

2. Using Program 10’s Growing Formula

3. console.log(line) Inside the Inner Loop

4. Blind parseInt(prompt())

5. rows > 26 Without a Policy

Edge Cases

Single letter

Empty pattern

rows < 0

Past Z

Non-numeric input

Lowercase variant

🎯 Practice Problems

1. Flip to Program 10

2. Forward letters (Program 12)

3. Safe input loop

4. Lowercase version

Example 1 — Fixed `'E'` down to `'A'`

Example 3 — `ch.repeat(repeat)`

🔎 Worked Walkthrough — `'E'` down to `'A'`

1. Printing `j` Instead of `i`

`rows < 0`