Build Your Logic from Scratch: Python Pattern Problems Explained. Star Pattern-2

#python #beginners #programming #coding

Ever looked at a pattern problem and thought, "Why can't I get this simple star pyramid to align properly?"
You're not alone. Pattern problems might look easy, but they’re the secret weapon for building powerful logic using loops — and today, we’re going to decode them step by step.

Pattern: Mirrored Right Angle Triangle Using Nested Loop in Python.

We’re going to build this simple star pattern and understand the logic behind nested loops:

Logic Overview

We're using two for loops:

The outer loop controls the rows
The inner loop controls the columns (stars)

        * 
      * * 
    * * * 
  * * * * 
* * * * *

Logic Overview

To form this pyramid:

You need spaces before star to centre-align them.
The number of stars increases with each row.

	1	2	3	4	5
1	(1,1)	(1,2)	(1,3)	(1,4)	*
2	(2,1)	(2,2)	(2,3)	*	*
3	(3,1)	(3,2)	*	*	*
4	(4,1)	*	*	*	*
5	*	*	*	*	*

As you see row increase the column decrease. (1,4),(2,3),(3,2),(4,1). or we can say,

Spaces increases and star decreases.

Code

row=5
for i in range(1,row+1):
    for j in range(1,row-i+1):
        print(" ",end=" ")
    for k in range(1,i+1):
        print("*",end=" ")
    print()

Explanation

row=5 this is for how many rows you want.
for i in range(1,row+1): This is the outer loop, which runs 5 times (from 1 to 5). Each loop iteration represents one row of the output.
for j in range(1,row-i+1): This inner loop is responsible for printing spaces before the stars. Why? To make the pattern right-aligned, each row needs less space than the previous one.
for k in range(1,i+1): This loop prints the stars * in each row.

Dry Run Table

i	j	k
Row(i)	Spaces(row-i+1)	Stars(i+1)	Output
1	4	1	*
2	3	2	* *
3	2	3	* * *
4	1	4	* * * *
5	0	5	* * * * *

Summary:
Outer loop (i): controls the number of rows, increasing each time
Inner loop (j): controls the trailing spaces.
Inner loop (k): prints the star.
end=" " prints stars on the same line
print() moves to the next line after each row

Pattern: Pyramid Using Nested Loop in Python

Output:

        * 
      * * * 
    * * * * * 
  * * * * * * * 
* * * * * * * * *

Step by Step Explanation

row=5
for i in range(1,row+1):
    for j in range(row-i):
        print(" ",end=" ")
    for k in range(2*i-1):
        print("*",end=" ")
    print()

	1	2	3	4	5	6	7	8	9
1					*
2				*	*	*
3			*	*	*	*	*
4		*	*	*	*	*	*	*
5	*	*	*	*	*	*	*	*	*

i->1,row+1, how many row you want.
j->row-i, it is for spaces, as it decreasing.
k2*i-1, it is to print star.

i	j	k
1	4	1
2	3	3
3	2	5
4	1	7
5	0	9

Summary
Outer loop (i): controls the number of rows, increasing each time
Inner loop (j): controlling the spaces which is decreasing each time.
Inner loop (k): It will print the star.
end=" " prints stars on the same line
print() moves to the next line after each row