Chapter 1: Understanding the Hollow Triangle Function

This section introduces the task of writing a function named hollow_triangle(string), which accepts a string input and outputs a hollow triangle pattern. Below are examples of the expected output based on different string inputs.

Example with string = "abcdefghijkl":

a

b l

c k

defghij

Example with string = "abcdefghij":

a

b *

c *

defghij

If the string does not contain enough characters to form a complete triangle, it will fill in with * characters. The function assumes that the input string will only contain letters and will have at least 7 characters.

For example, if the input is:

string = "abcdefgh"

The output will be:

a

b h

cdefg

Challenge — Solve This in One Line of Python Code

Before diving into the solution, take a moment to attempt solving this challenge.

Steps to Arrive at the Solution

Initially, we must break down the problem into manageable parts before condensing it into a single line. Here’s the step-by-step process:

1. Adjust the String Length: Add * characters to the end of the string until its length is a multiple of 4, as only these lengths can create a perfect triangle.
2. Determine the Triangle Height: Calculate how tall the hollow triangle will be.
3. Print the Triangle: Output the top, middle, and bottom sections of the triangle.

Here’s a multi-line solution for better clarity:

def hollow_triangle(string):

if len(string) % 4 > 0:

string += '*' * (4 - len(string) % 4)

height = len(string) // 4 + 1

print((height - 1) * ' ', string[0], sep='')

for i in range(1, height - 1):

print((height - i - 1) * ' ', string[i], ' ' * (2 * i - 1), string[-i], sep='')

print(string[i + 1:-i])

Converting to a One-Liner

To streamline the function into one line, we can implement the following:

def hollow_triangle(S):

S = S.ljust(len(S) + (n := (4 - len(S)) % 4) * bool(n), '*');

print(((H := (len(S) // 4 + 1)) - 1) * ' ' + S[0]);

[print((H - i - 1) * ' ', S[i], (2 * i - 1) * ' ', S[-i], sep='') for i in range(1, H - 1)];

print(S[H - 1:-H + 2])

Conclusion

This brief overview clarifies how to achieve a hollow triangle pattern in Python using a concise one-liner function.

The second video provides additional insights and examples on how to simplify your Python code effectively.

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