Table of Contents

SNo.	Link
1	Right-angled Triangle
2	Inverted Right-angled Triangle
3	Centered Half Pyramid

1. Right-angled Triangle

#Expected Output for number of rows = 5
*
**
***
****
*****

To build the logic, always represent the pattern in a tabular format.

R\C	j=1	j=2	j=3	j=4	j=5
i=1	*
i=2	*	*
i=3	*	*	*
i=4	*	*	*	*
i=5	*	*	*	*	*

• We can observe that '*' is being printed up to i<=j
  
• Usually we need two loops for printing i.e. i^th loop for rows and j^th loop for columns (Basic understanding)
  
• i^th loop iterates up to n (inclusive) where as j^th loop iterates up to i (inclusive)

Code for it can be written as follows:

n=int(input()) #no. of rows
for i in range(1,n+1):
    for j in range(1,i+1):
        print('*',end='')
    print()

• end is an optional argument for print(), it tells what should be printed at the end of the output.
• It is used to bypass the default \n argument allowing '*' to appear side by side.
• we use 'print()' as a \n allowing subsequent iterations to print in fresh rows.

Output without using end and print()

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

Since python supports String Multiplication, above code can also be written as follows:

n=int(input())
for i in range(1, n+1):
    print("*" * i)

at i=1 it prints 1 '*' (1 * '*' = *)
at i=2 it prints 2 '*' (2 * '*' = **) and so on..

2. Inverted Right-angled Triangle

#Expected Output for number of rows = 5
    *
   **
  ***
 ****
*****

Tabular representation:

R\C	j=1	j=2	j=3	j=4	j=5
i=1					*
i=2				*	*
i=3			*	*	*
i=4		*	*	*	*
i=5	*	*	*	*	*

To solve this, check where the '*' is being printed (i.e. no. of white spaces).

• at i=1, 4 white spaces and 1 '*'
• at i=2, 3 white spaces and 2 '*'
• at i=3, 2 white spaces and 3 '*'
• at i=4, 1 white spaces and 4 '*'
• at i=5, 0 white spaces and 5 '*'

White spaces are being decreased where as '*' as being increased row by row.
=> no. of white spaces: n-i and no. of '*' : i

n=int(input())
for i in range(1,n+1):
    for j in range(n-i): #Loop runs for n-i times, since we have n-i white spaces
        print(' ',end='')
    for k in range(i): #Loop runs for i times, since we have i '*'
        print('*',end='')
    print()

It can also be wriiten as:

n=int(input())
for i in range(1,n+1):
    print(' '*(n-i)+'*'*i) #String concatenation

3. Centered Half Pyramid

#Expected Output
    *
   * *
  * * *
 * * * *
* * * * *

• It is similar to Inverted Right-angled Triangle
• Add a space after printing * to acheive the output.

Tabular representation:

				*	W
			*	W	*	W
		*	W	*	W	*	W
	*	W	*	W	*	W	*	W
*	W	*	W	*	W	*	W	*

Here, W is the white space.

n=int(input())
for i in range(1,n+1):
    for j in range(n-i):
        print(' ',end='')
    for k in range(i): 
        print('*',end=' ')
    print()

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