Inverted Right-Aligned Right-Angled Triangle Star Pattern in Python

Q: How does the program create an inverted right-aligned triangle?

For each row i from 1 to rows, print i minus 1 spaces, then print stars with k running from i to rows inclusive. That prints rows minus i plus 1 stars. Row 1 has no spaces and rows stars; each later row adds one space and removes one star while keeping the same right edge.

Q: Why use k from i to rows for stars?

The range i through rows has length rows minus i plus 1, which matches the star count. An equivalent loop is k from 1 to rows minus i plus 1, or k from rows down to i.

Q: What is the difference between this pattern and Program 3?

Program 3 uses (rows - i) spaces and stars 1 through i. Program 4 uses (i - 1) spaces and stars i through rows. Same right alignment; star counts grow in Program 3 and shrink in Program 4.

Q: How is this related to Program 2?

Program 2 is left-aligned with shrinking stars. Program 4 adds growing leading spaces so the same shrinking star counts stay flush on the right.

Q: What is the time complexity?

O(n²) for n rows. Each row prints on the order of n characters; there are n rows.

Q: Can I use string multiplication for spaces and stars?

Yes. print(" " * (i - 1) + "*" * (rows - i + 1)) builds each row without explicit inner character loops.

Q: Why is the space loop range(1, i) instead of range(1, i + 1)?

range(1, i) prints exactly i - 1 spaces. Using range(1, i + 1) would add one extra space and break the right edge.

Q: How should I read the row count safely?

Wrap int(input()) in try/except ValueError so bad input does not crash the script.

Beginner

⏱️ 9 min read

📚 Updated: Aug 2026

🎯 3 Code Examples

🚀 Live Preview

Spaces + Decreasing Stars

Inverted right-aligned right-angled triangle star pattern output in Python programming

Overview

What You’ll Learn

The inverted right-aligned triangle keeps a flush right edge like Program 3, but star counts shrink like Program 2: widest line on top. This tutorial covers the space and star formulas, a live preview, algorithm steps, worked Python examples, edge cases, and complexity.

Shape Rule

Wide on top

First line has rows stars; each next line has one fewer, flush right.

Space Loop

i - 1

Print i - 1 spaces (none on row 1) so the block stays right-aligned.

Star Loop

i..rows

k from i to rows prints rows - i + 1 stars.

Fixed Width

n chars/row

Every row: (i - 1) + (rows - i + 1) = rows characters.

Live Preview

1–20 rows

Pick a row count and draw the inverted right-aligned triangle instantly.

O(n²)

Complexity

n rows × Θ(n) characters each — O(n²) time, O(1) extra space.

Introduction

An inverted right-aligned triangle has the widest star run on the first line and shrinks by one star each row, while the right edge stays flush.

It merges Program 2’s decreasing star counts with Program 3’s right alignment: growing spaces (i - 1) plus shrinking stars (rows - i + 1).

Why it matters?

It completes the four basic corner triangles (left / inverted / right / inverted-right). After this, centered pyramids are a small jump.

Key Highlights

Growing Spaces

Row i has i - 1 leading spaces.

Shrinking Stars

rows - i + 1 stars (or k = i..rows).

Same Right Edge

Flush-right like Program 3, inverted like Program 2.

Series Capstone

Last of the four basic right-angled variants.

In short: for each row i, print i - 1 spaces, then rows - i + 1 stars, then a newline.

Foundation

📝 Problem & Approach

Given a positive integer rows, print an inverted right-aligned right-angled triangle of * characters with rows lines.

Python

# First 5 rows (spaces shown as ·)
# *****
# ·****
# ··***
# ···**
# ····*

Inputs & Outputs

Item	Type	Description
`rows`	int	Number of lines (typically ≥ 1). Also the width of each line.
Printed output	text	Right-aligned rows: `(i - 1)` spaces + `(rows - i + 1)` stars.

Minimal workflow

Pseudocode

for i from 1 to rows:
    for j from 1 to (i - 1):     // range(1, i) in Python
        print " "
    for k from i to rows:        // rows - i + 1 stars
        print "*"
    print newline

Approach comparison

Approach	Idea	Best for
`k = i..rows`	Star loop bound encodes the count	Matches classic textbook listings
`1..(rows - i + 1)`	Explicit star count variable	Clearer when explaining formulas

Cheat Sheet

⚡ Quick Reference

Goal	Pattern
Walk each row	`for i in range(1, rows + 1):`
Leading spaces	`for j in range(1, i): print(" ", end="")`
Stars via range	`for k in range(i, rows + 1): print("*", end="")`
Stars via count	`for k in range(1, rows - i + 2):`
Width check	`(i - 1) + (rows - i + 1) == rows`
String shortcut	`print(" " * (i - 1) + "" (rows - i + 1))`

Compare

📋 Programs 1–4 at a Glance

Four corner variants — alignment and star growth differ.

Program 1

left grow

Only i stars — no spaces

Program 2

left shrink

Countdown / rows - i + 1 stars

Program 3

right grow

rows - i spaces, i stars

This page

right shrink

i - 1 spaces, rows - i + 1 stars

Context

When This Pattern Shows Up

Reach for this figure when combining right alignment with shrinking star counts.

After Programs 2 and 3
Natural merge of invert + right-align skills.
Two-formula drills
Spaces grow while stars shrink — opposite trends in one row.
Pyramid stepping stone
Next: Program 5 centers with odd star counts.
Bound-style practice
Compare k = i..rows with an explicit star count loop.
Not a UI layout tool
Console teaching pattern — not how you build app screens.

Key benefit: one pattern that locks in growing padding and shrinking fill while keeping a fixed right edge.

Interactive

🔮 Live Preview

Choose a row count between 1 and 20 and draw the inverted right-aligned triangle in the browser.

Hands-On

Examples Gallery

Three complete Python programs — classic k = i..rows loops, console input, and a "*" * shortcut. Click View Output to reveal sample console results.

📚 Getting Started

Print five inverted right-aligned rows with nested loops.

Example 1 — Fixed `rows = 5`

Space loop with range(1, i), star loop with k from i to rows.

Python

rows = 5

for i in range(1, rows + 1):
    for j in range(1, i):
        print(" ", end="")
    for k in range(i, rows + 1):
        print("*", end="")
    print()

How It Works

When i = 1, print 0 spaces and stars for k = 1..5 (five stars). When i = 5, print 4 spaces and stars for k = 5..5 (one star). Every row has exactly 5 characters before the newline.

📈 Practical Variant

Let the user choose the height at runtime.

Example 2 — User Input Version

Read rows with input() and int() (wrap in try/except ValueError in real apps).

Python

rows = int(input("Enter the number of rows: "))

for i in range(1, rows + 1):
    for j in range(1, i):
        print(" ", end="")
    for k in range(i, rows + 1):
        print("*", end="")
    print()

How It Works

Same space/star core as Example 1; only the source of rows changes. Non-numeric input raises ValueError with bare int(input()) — use try/except for safer labs.

⚡ Shortcut Style

Same shape with explicit star count and string multiplication.

Example 3 — `"" ` + Explicit Count

Build padding and stars from the formulas directly.

Python

rows = 5

for i in range(1, rows + 1):
    spaces = i - 1
    stars = rows - i + 1
    print(" " * spaces + "*" * stars)

How It Works

Naming spaces and stars makes the invert-vs-align story obvious. Keep the k = i..rows version when you want the classic listing style.

🧠 How the Algorithm Prints Rows

Set up

Set rows. Use i for the row, j for spaces, k for stars.

Setup

Outer loop

for i in range(1, rows + 1): — widest when i == 1, one star when i == rows.

Row

Indent spaces

for j in range(1, i): print(" ", end="") prints i - 1 spaces.

Align

Stars then newline

for k in range(i, rows + 1): print("*", end="") then print(). Width stays rows.

Stars

Inverted, still right-aligned

Star total n(n+1)/2; O(n²) time, O(1) extra space.

Trace

🔎 Worked Walkthrough — `rows = 4`

Trace spaces, stars, and total width for each outer-loop value of i.

`i`	Spaces `i - 1`	Stars `rows - i + 1`	`k` range	Printed row
`1`	0	4	`1..4`	`****`
`2`	1	3	`2..4`	`***`
`3`	2	2	`3..4`	`**`
`4`	3	1	`4..4`	`*`

Check: every row has width 4. Star total: 4+3+2+1 = 10.

Use Cases

Where this inverted right-aligned pattern shows up beyond the homework prompt.

1. Completing the Quartet

Finish left / invert / right / invert-right before pyramids.

Example: compare all four for rows = 5.

2. Opposite Trends

Spaces increase as stars decrease — strong formula practice.

Example: flip only one formula and watch the edge break.

3. Bound vs Count Style

Rewrite k = i..rows as 1..(rows - i + 1).

Example: same output, different loop headers.

4. Recover Program 3

Swap to rows - i spaces and 1..i stars.

Example: one edit each way between the two pages.

5. Pyramid Prep

Next patterns reuse padding plus multi-star runs.

Example: Program 5 uses 2*i - 1 stars.

6. Input Validation Labs

Pair with input validation and positive-row checks.

Example: reject rows <= 0 and re-prompt.

Pro Tip: say “Program 3 with star growth flipped” before coding — spaces grow, stars shrink.

Advantages

Why this pattern earns a place after Programs 1–3.

1. Combines Two Known Skills
Invert (Program 2) + right-align (Program 3) in one figure.
2. Easy Width Check
Every row length equals rows — bugs show up immediately.
3. Two Equivalent Star Loops
Range style or count style — both are interview-friendly.
4. O(1) Extra Memory
Streaming output needs only loop counters.

Pro Tip: lead with the formulas spaces = i - 1 and stars = rows - i + 1, then pick a loop style.

Usage Tips

Small habits that keep this pattern clean.

1. Keep range(1, i) for Spaces
j <= i adds an extra space and shifts the right edge.
2. Use Real Spaces, Not Tabs
Tabs break alignment across fonts and editors.
3. Wrap int(input()) in try/except
Avoid crashes when the user types letters instead of a number.
4. Verify Width = rows
Check tip and last rows: spaces + stars must sum to rows.
5. Dry-Run One Small n
Trace rows = 4 on paper before coding larger demos.

Pro Tip: if the first line has leading spaces, your space formula is wrong — row 1 must use i - 1 = 0 spaces.

Common Pitfalls

Mistakes that commonly break inverted right-aligned triangles.

1. Using Program 3’s Formulas
rows - i spaces and 1..i stars grows instead of shrinks.
→ Use i - 1 spaces and rows - i + 1 stars.
2. range(1, i + 1) Instead of range(1, i)
One extra space per row shifts the right edge leftward.
→ Space loop must run exactly i - 1 times.
3. Star Loop 1..i
That is Program 3 again — growing, not inverted.
→ Use k = i..rows or count rows - i + 1.
4. Mixing Tabs With Spaces
Alignment looks fine in one editor and broken in another.
→ Always print the space character " ".
5. Blind int(input())
Letters or empty input throw ValueError.
→ Catch ValueError and re-prompt on failure.

Edge Cases

Check these inputs before calling the solution done.

rows = 1

Single star

0 spaces + 1 star — same as the other triangle pages for n = 1.

rows = 0

Empty pattern

Outer loop never runs — print nothing or show a message.

Negative

`rows < 0`

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

Large n

Wide first line

First line has n stars — fine for labs; may wrap on tiny terminals.

Bad input

Non-numeric ReadLine

int(input()) raises ValueError — validate first.

First row

`i == 1`

Space loop must not run; only a full run of stars.

Drill

🎯 Practice Problems

Try these variations to lock in the pattern.

1. Flip back to Program 3

Use rows - i spaces and 1..i stars
Confirm the staircase grows again

2. Rewrite the star loop

Replace k = i..rows with count rows - i + 1
Match Example 3’s clarity

3. Safe input loop

Validate input until rows >= 1
Then draw the pattern

4. Center pyramid next

Keep leading spaces; use odd star counts
Continue with Program 5

Important

Notes

Program 3 flipped. Same right edge; star counts shrink instead of grow.
Every row has width rows: (i - 1) + (rows - i + 1) = rows.
Validate rows > 0 for interactive programs; rows = 1 prints a single star.
Next: Program 5 centers a full pyramid with 2 * i - 1 stars.

Quick Takeaway: print i - 1 spaces, then rows - i + 1 stars — inverted and flush right.

Analysis

⏱️ Time and Space Complexity

Program	Time	Extra space
Nested space/star loops (Examples 1–2)	`O(rows²)`	`O(1)`
`"" ` shortcut (Example 3)	`O(rows²)`	`O(rows)` temporary per row string

Each of n rows prints Θ(n) characters (spaces + stars).

Wrap Up

🎉 Conclusion

The inverted right-aligned triangle is Program 3 with star growth flipped: i - 1 spaces and rows - i + 1 stars. With Programs 1–4 you can print any of the four basic right-angled variants.

Practice the three examples above, then continue to the center-aligned pyramid.

Spaces grow, stars shrink, width stays rows — keep range(1, i) for spaces, and validate row counts when reading input.

View Examples Gallery Continue to Center Pyramid

Pro Tips

💡 Best Practices

✅ Do

Explain i - 1 spaces and rows - i + 1 stars before coding
Use range(1, i) (not range(1, i + 1)) for the space loop
Know both k = i..rows and the explicit count form
Check that each row has width rows
Use try/except ValueError for interactive demos

❌ Don’t

Reuse Program 3’s space/star formulas here
Add an extra space with j <= i
Print stars with 1..i when you meant inverted
Ignore bad console input in user-facing demos
Skip the rows = 1 edge case

Summary

Key Takeaways

Knowledge Unlocked

Five things to remember about this inverted right-aligned pattern

Print the flush-right inverted triangle the beginner-friendly way.

Core concepts

◁ 01

Rule

Wide on top, flush right

Definition

␣ 02

Spaces

i - 1

Formula

* 03

Stars

rows - i + 1

Formula

= 04

Width

Always rows

Check

O 05

Complexity

O(n²) time

Analysis

❓ Frequently Asked Questions

How does the program create an inverted right-aligned triangle?

For each row i from 1 to rows, print i minus 1 spaces, then print stars with k running from i to rows inclusive. That prints rows minus i plus 1 stars. Row 1 has no spaces and rows stars; each later row adds one space and removes one star while keeping the same right edge.

Why use k from i to rows for stars?

The range i through rows has length rows minus i plus 1, which matches the star count. An equivalent loop is k from 1 to rows minus i plus 1, or k from rows down to i.

What is the difference between this pattern and Program 3?

Program 3 uses (rows - i) spaces and stars 1 through i. Program 4 uses (i - 1) spaces and stars i through rows. Same right alignment; star counts grow in Program 3 and shrink in Program 4.

How is this related to Program 2?

Program 2 is left-aligned with shrinking stars. Program 4 adds growing leading spaces so the same shrinking star counts stay flush on the right.

What is the time complexity?

O(n²) for n rows. Each row prints on the order of n characters; there are n rows.

Can I use string multiplication for spaces and stars?

Yes. print(" " * (i - 1) + "*" * (rows - i + 1)) builds each row without explicit inner character loops.

Why is the space loop range(1, i) instead of range(1, i + 1)?

range(1, i) prints exactly i - 1 spaces. Using range(1, i + 1) would add one extra space and break the right edge.

How should I read the row count safely?

Wrap int(input()) in try/except ValueError so bad input does not crash the script.

Did you Know? 🔊

This pattern merges Program 2’s shrinking star count with Program 3’s right alignment. Every row still has width rows: (i - 1) + (rows - i + 1) = rows.

Continue to Center-Aligned Pyramid

Use leading spaces and odd star counts (2 * i - 1) to print a full pyramid.

Program 5 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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Python Star Pattern 3 — Right-Aligned Triangle Python Star Pattern 5 — Center Pyramid

Inverted Right-Aligned Right-Angled Triangle Star Pattern in Python

What You’ll Learn

Shape Rule

Space Loop

Star Loop

Fixed Width

Live Preview

O(n²)

Introduction

Why it matters?

Growing Spaces

Shrinking Stars

Same Right Edge

Series Capstone

📝 Problem & Approach

Inputs & Outputs

Minimal workflow

Approach comparison

⚡ Quick Reference

📋 Programs 1–4 at a Glance

When This Pattern Shows Up

After Programs 2 and 3

Two-formula drills

Pyramid stepping stone

Bound-style practice

Not a UI layout tool

🔮 Live Preview

Examples Gallery

📚 Getting Started

Example 1 — Fixed rows = 5

How It Works

📈 Practical Variant

Example 2 — User Input Version

How It Works

⚡ Shortcut Style

Example 3 — "*" * + Explicit Count

How It Works

🧠 How the Algorithm Prints Rows

Set up

Outer loop

Indent spaces

Stars then newline

Inverted, still right-aligned

🔎 Worked Walkthrough — rows = 4

Use Cases

1. Completing the Quartet

2. Opposite Trends

3. Bound vs Count Style

4. Recover Program 3

5. Pyramid Prep

6. Input Validation Labs

Advantages

1. Combines Two Known Skills

2. Easy Width Check

3. Two Equivalent Star Loops

4. O(1) Extra Memory

Usage Tips

1. Keep range(1, i) for Spaces

2. Use Real Spaces, Not Tabs

3. Wrap int(input()) in try/except

4. Verify Width = rows

5. Dry-Run One Small n

Common Pitfalls

1. Using Program 3’s Formulas

2. range(1, i + 1) Instead of range(1, i)

3. Star Loop 1..i

4. Mixing Tabs With Spaces

5. Blind int(input())

Edge Cases

Single star

Empty pattern

rows < 0

Wide first line

Non-numeric ReadLine

i == 1

🎯 Practice Problems

1. Flip back to Program 3

2. Rewrite the star loop

3. Safe input loop

4. Center pyramid next

Example 1 — Fixed `rows = 5`

Example 3 — `"" ` + Explicit Count

🔎 Worked Walkthrough — `rows = 4`

1. Keep `range(1, i)` for Spaces

3. Wrap `int(input())` in try/except

4. Verify Width = `rows`

2. `range(1, i + 1)` Instead of `range(1, i)`

3. Star Loop `1..i`

`rows < 0`

`i == 1`