Python Inverted Triangle Star Pattern (Right-Angled)
Beginner
6 min read
Updated: Sep 2026
3 programs
Live preview
Definition
What Is This Pattern?
An inverted right-angled triangle star pattern prints a left-aligned upside-down staircase of * characters: the first row has rows stars, and each next row has one fewer down to 1.
Remember
Rule: on outer value i, print i stars (i counts down)
*****
****
***
**
* ← 5 rows
In Python you solve it with two nested for loops: the outer loop counts from rows down to 1, the inner loop prints stars for the current i, then bare print() moves to the next line. It is the mirror of Program 1 — same inner loop, reversed outer direction.
Approach
How to Solve It
Two ways to emit the same shape — start with a countdown outer loop, then optionally use a forward formula or string multiplication.
Method
Idea
Best for
Countdown outer
i = rows..1, inner prints i stars via print(..., end="")
Learning, interviews, clearest invert of Program 1
Forward + formula
i = 1..rows, print rows - i + 1 stars
When you prefer ascending counters
"*" * i
Build a whole row in one call while counting down
Shorter demos once loops click
Pseudocode
Pseudocode
for i from rows down to 1:
for j from 1 to i:
print "*" (no newline)
print newline
Print stars without a newline, then end the row once.
Try it
Live Preview
Change the row count and the inverted triangle updates instantly — including the triangular star total.
Whole numbers from 1 to 20. Tap a chip or type a value — the preview redraws as you go. The first line has that many stars.
Live result5 rows · 15 stars
*****
****
***
**
*
Trace
Worked Walkthrough — rows = 4
Trace each outer-loop value of i as it counts down, and count how many times the inner loop runs.
i
Inner j
Printed row
Stars
4
1..4
****
4
3
1..3
***
3
2
1..2
**
2
1
1..1
*
1
Total star prints: 4 + 3 + 2 + 1 = 10 = 4×5/2. Same triangular sum as Program 1 — time is still O(n²).
Code
Python Programs
Three complete programs: fixed rows (countdown), input(), and a "*" * i shortcut. Use View Output to reveal sample results.
Example 1 — Fixed rows = 5
Hard-coded height with a countdown outer loop — the clearest invert of Program 1.
Python
rows = 5
for i in range(rows, 0, -1):
for j in range(1, i + 1):
print("*", end="")
print()
Output
*****
****
***
**
*
How It Works
1. Set height.rows = 5 means the triangle has five lines; the first line has five stars.
2. Outer loop counts down.i runs from rows down to 1 via range(rows, 0, -1).
3. Inner loop prints stars. For each i, j runs from 1 to i, so the current row gets exactly i stars via print("*", end="").
4. Break the line. Bare print() after the inner loop starts the next (shorter) row.
When i = 5 you get *****; when i = 4 you get ****; and so on down to one star.
Example 2 — User Input Version
Read the row count at runtime. Prefer a try / except in real apps (shown in the tip below).
Python
rows = int(input("Enter the number of rows: "))
for i in range(rows, 0, -1):
for j in range(1, i + 1):
print("*", end="")
print()
Output (when user enters 7)
Enter the number of rows: 7
*******
******
*****
****
***
**
*
How It Works
1. Prompt and read.input() returns a string; int(...) converts it to a whole number.
2. Same nested-loop core. Only the source of rows changes — the countdown print logic matches Example 1.
3. Safer input tip.int(input()) raises ValueError on letters. Prefer:
Safer input
raw = input("Enter the number of rows: ").strip()
try:
rows = int(raw)
except ValueError:
print("Enter a positive whole number.")
raise SystemExit
if rows < 1:
print("Enter a positive whole number.")
raise SystemExit
Example 3 — "*" * i
Build each row in one call while counting down — same shape, no explicit inner star loop.
Python
rows = 5
for i in range(rows, 0, -1):
print("*" * i)
Output
*****
****
***
**
*
How It Works
1. One outer loop. Still walk i from rows down to 1.
2. Build the row."*" * i creates a string of length i filled with stars.
3. Print and advance.print(...) prints that string and ends the line.
Learn the two-loop version first (Examples 1–2) so you can explain both bounds in an interview; treat this as a polish shortcut afterward.
Edge Cases & Pitfalls
Check these before calling the solution done.
Wrong direction
Upright instead of inverted
If you use range(1, rows + 1) instead of range(rows, 0, -1), you get Program 1’s growing triangle. For the inverted shape, count down — or use rows - i + 1 stars with a forward loop.
print() inside
Column of stars
If bare print("*") is inside the inner loop, each star lands on its own line. Use print("*", end="") for stars; print() only after the inner loop.
j to rows
Rectangle, not triangle
Inner bound must be range(1, i + 1) (or length rows - i + 1). Looping to rows every time prints a filled rectangle.
No print()
One endless line
Omitting the row break glues every star onto a single line.
rows = 1
Single star
Output is just * on one line — a good sanity check (same as Program 1).
rows ≤ 0
Empty output
Outer loop never runs. Validate and re-prompt for interactive programs.
Bad input
Catch ValueError
int(input()) throws on letters — prefer try / except ValueError.
Analysis
Time and Space Complexity
Program
Time
Extra space
Nested loops (Examples 1–2)
O(rows²)
O(1)
"*" * i (Example 3)
O(rows²)
O(rows) per temporary row string
Total stars printed = n + (n-1) + … + 1 = n(n+1)/2, which is still quadratic in n — identical to Program 1.
Remember
Key Takeaways
Rule: outer value i prints exactly i stars, with i counting from rows down to 1.
Same as Program 1: only the outer loop direction changes; the inner star loop stays j = 1..i.
Break the row: call bare print() only after the inner loop.
Complexity:O(n²) time from the triangular star count; O(1) extra space for nested loops.
One line: for i from rows down to 1, print i stars with end="", then call print().
Frequently Asked Questions
The outer loop runs i from rows down to 1. For each i, the inner loop prints i stars. The first output line uses i equal to rows so it is the longest; each later line has a smaller i, so the triangle points downward.
Program 1 uses for i in range(1, rows + 1) so stars grow. This program uses for i in range(rows, 0, -1) so stars shrink. The inner loop still runs j from 1 to i.
Yes. Use for i in range(1, rows + 1) and print (rows - i + 1) stars in the inner loop. Both styles produce the same shape.
print("*", end="") stays on the same line. print() ends the current line. Stars use end=""; the row break uses print() after the inner loop.
O(n²) for n rows. Total stars are still n(n+1)/2, same as the upright triangle.
Yes. print("*" * i) prints a full row in one call while i counts down.
Wrap int(input()) in try/except ValueError and require rows >= 1 so bad input does not crash the script.
The outer loop never runs, so nothing is printed. Validate and prompt again if you want a clear user message.
🤔
Did you know?
This inverted triangle uses the same inner loop as Program 1 — only the outer loop direction changes. Total stars stay n(n+1)/2, so complexity is still O(n²).
