Approach for Hollow pattern

 Approach for Hollow pattern problem

In this cheat sheet, let's see how to print the Hollow right-angled triangle pattern

Below is the pattern of the Hollow right-angled triangle

*

* *

* *

* *

* *

* *

* * * * * * *

Now, let's see how to print the 7x7 hollow right-angled triangle pattern.

Logical approach:

Note

In the above image, each empty box contains 2 spaces (double space '  '), and each star is followed by a space ('* ').

• While writing the code,
  • you need to print * as '* '(star followed by space).
  • you need to print 2 spaces('  ') in place of a single space.

The above image is the 7x7 pattern of the hollow right-angled triangle

• The first row has 6 spaces and has one star.
• The second row has 5 spaces and the first star and the second star.
• The third, fourth, fifth, and sixth rows have decreasing spaces, followed by the first star with increasing hollow spaces, then the second star.
• The last row has 7 stars.

Here in this problem

• space is denoted as the '  ' ( Double Spaces)

• star set denoted as the '* ' (Star is followed by space)

Let's now discuss line by line

Pattern	Line Number	Number of Spaces
*	First line	6 Double spaces	1st star
* *	Second line	5 Double spaces	1st star-set('* ')	2nd Star
*     *	Third line	4 Double spaces	1st star-set('* ')	1 Hollow spaces	2nd star
*        *	Fourth line	3 Double spaces	1st star-set('* ')	2 Hollow spaces	2nd star
*             *	Fifth line	2 Double spaces	1st star-set('* ')	3 Hollow spaces	2nd star
*                  *	Sixth line	1 Double spaces	1st star-set('* ')	4 Hollow spaces	2nd star
*  *  *  *  *  *  *	Seventh line	0 Double spaces	7 star-sets('* ')

Now, let's see how to print the above pattern using a python program.

• We can divide the above pattern logic into 3 parts
  • Part 1: we have spaces and star('*') in first line
  • Part 2: we have spaces, star, hollow spaces, star (middle lines)
  • Part 3: we have star set('* ') in the last line

Code:

• We can use the For loop and if-elif-else statement to execute the particular part.

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N = 7

for i in range(0, N):

if i == 0: # part- 1 logic

print(' '* (N-1) + '*')

elif i == N - 1: # part- 3 logic

print('* ' * N)

else: # part- 2 logic

left_spaces = ' ' * (N -i-1)

hollow_spaces = (' ' * ( i - 1))

print(left_spaces + '* ' + hollow_spaces + '*')

PYTHON

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Now let's see the explanation of the for loop execution, step by step:

Part - 1 (first line):

i = 0 The first row has 6 spaces followed by one star. In order to get 6 no. of spaces, we must subtract 1 from the

N

value.

spaces = ' ' * (N-1) = 6 // Here N value is 7

Output is

1

*

Part - 2 (logic to print the Second line to Sixth line):

i = 1 In the second row, we have 5 spaces followed by the first star and hallow spaces followed by the second star. In order to get 5 no.of spaces, we must subtract 1 and

i

value from the

N

value.

spaces = ' ' * (N-i-1) = 5

hollow_spaces = (' ' * ( i - 1)) = 0

Output is

*

* *

i = 2 In the third row, we have 4 spaces followed by the first star and hallow spaces followed by the second star. In order to get 4 no.of spaces, we must subtract 1 and

i

value from the

N

value.

spaces = ' ' * (N-i-1) = 4

hollow_spaces = (' ' * ( i - 1)) = 1

Output is

*

* *

* *

i = 3 In the fourth row, we have 3 spaces followed by the first star and hallow spaces followed by the second star. In order to get 3 no.of spaces, we must subtract 1 and

i

value from the

N

value.

spaces = ' ' * (N-i-1) = 3

hollow_spaces = (' ' * ( i - 1)) = 2

Output is

*

* *

* *

* *

i = 4 In the fifth row, we have 2 spaces followed by the first star and hallow spaces followed by the second star. In order to get 2 no.of spaces, we must subtract 1 and

i

value from the

N

value.

spaces = ' ' * (N-i-1) = 2

hollow_spaces = (' ' * ( i - 1)) = 3

Output is

*

* *

* *

* *

* *

i = 5 In the sixth row, we have 1 space followed by the first star and hallow spaces followed by the second star. In order to get 1 space, we must subtract 1 and

i

value from the

N

value.

spaces = ' ' * (N-i-1) = 1

hollow_spaces = (' ' * ( i - 1)) = 4

Output is

*

* *

* *

* *

* *

* *

Part - 3 (Seventh line):

i = 6

stars = '* ' * N

Output is

*

* *

* *

* *

* *

* *

* * * * * * *