How are the left and right halves generated?

The first loop prints j from 1 to 5 but only shows digits when j <= i (otherwise spaces). The second loop prints k from 5 down to 1 but only shows digits when k <= i (otherwise spaces).

Why are there spaces in the middle?

For smaller i values, most positions are printed as spaces to keep the left and right halves separated. On the last row, i = 5, so no spaces remain and the halves touch.

Can I change the size of the pattern?

Yes. Use rows as input and loop j from 1..rows and k from rows..1. Print digits only when the loop variable is <= i; otherwise print spaces.

What is the time complexity of this program?

O(n^2) for n rows, because each row prints 2n positions using two loops.

Split Mirror Number Pattern in Python

Q: Why are there spaces in the middle?

For smaller i values, most positions are printed as spaces to keep the left and right halves separated. On the last row, i = 5, so no spaces remain and the halves touch.

Q: Can I change the size of the pattern?

Yes. Use rows as input and loop j from 1..rows and k from rows..1. Print digits only when the loop variable is <= i; otherwise print spaces.

Q: What is the time complexity of this program?

O(n^2) for n rows, because each row prints 2n positions using two loops.

Beginner

⏱️ 6 min read

📚 Updated: Aug 2025

🎯 2 Code Examples

Nested Loops

Split mirror number pattern output (1 1, 12 21, 123 321, 1234 4321, 1234554321) in Python

What You’ll Learn

How to print a split mirror number pattern in Python, where the left side grows and the right side mirrors it:

1 1
12 21
123 321
1234 4321
1234554321

This pattern uses two loops per row and prints spaces when the current position is beyond the row width.

⭐ Pattern Output

For 5 rows, the pattern looks like this:

Output

Complete Python Program

Each row prints the left half (1..i) with spaces, then prints the right half (i..1) with spaces, creating a split mirror effect.

Python

for i in range(1, 6):
    for j in range(1, 6):
        if j <= i:
            print(j, end="")
        else:
            print(" ", end="")
    for k in range(5, 0, -1):
        if k <= i:
            print(k, end="")
        else:
            print(" ", end="")
    print()

🧠 How It Works

Outer loop controls rows

for i in range(1, 6) prints 5 rows and sets how many digits are visible on each side.

Row control

Left loop prints 1..i

for j in range(1, 6) prints j only when j <= i. Otherwise it prints a space, keeping the left block width constant.

Left half

Right loop prints i..1

for k in range(5, 0, -1) prints k only when k <= i. Otherwise it prints spaces to maintain alignment.

Right half

Print a newline

print() moves to the next row.

Line break

1        1
12      21
123    321

Split mirror effect

Each row prints \(2n\) positions (here \(n=5\)), so overall runtime is O(n²) for \(n\) rows.

Variation — User Input Version

Choose the number of rows. This version automatically scales the left and right halves.

Python

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

for i in range(1, rows + 1):
    for j in range(1, rows + 1):
        if j <= i:
            print(j, end="")
        else:
            print(" ", end="")
    for k in range(rows, 0, -1):
        if k <= i:
            print(k, end="")
        else:
            print(" ", end="")
    print()

💡 Tips for Enhancement

Try These

Validate input (reject rows < 1) before printing
Replace spaces with dots (.) to visualize the alignment grid
Center the whole output by adding leading spaces per row
Add a separator between halves (like |)
Build each row as a string for better performance on large sizes

Avoid

Mixing end="" and default prints in the same row
Changing loop bounds without updating expected output
Forgetting the newline print at the end of each row
Assuming user input is always valid (wrap int() conversion if needed)

Key Takeaways

Two loops build the left and right halves of the mirror.

Spaces keep each half a constant width until the last row.

The final row has no spaces in the middle, forming 1234554321.

Overall runtime is O(n²) due to nested loops.

❓ Frequently Asked Questions

Why does the last row become a full mirror string?

When i reaches the maximum (5), both loops print all digits (no spaces), so the left half is 12345 and the right half is 54321, forming 1234554321.

How do I reduce or increase the gap in the middle?

The gap is created by printing spaces in positions where the index is greater than i. Changing the total width (rows) changes how many spaces appear.

Can I use this technique for stars or letters?

Yes. Replace the printed digits with stars or letters, and keep the same spacing logic to preserve the split mirror structure.

What is the time complexity?

O(n²) for \(n\) rows, since each row uses two loops of length \(n\).

Explore More Python Number Patterns!

Try more mirror and gap-based patterns to improve your loop control.

All Number Patterns →

Did you know?

Split patterns are a practical way to learn “print value else print space” logic, which is the foundation of many alignment and formatting tasks.

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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