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48 changes: 48 additions & 0 deletions maths/special_numbers/happy_number.py
Original file line number Diff line number Diff line change
@@ -0,0 +1,48 @@
def is_happy_number(number: int) -> bool:
"""
A happy number is a number which eventually reaches 1 when replaced by the sum of
the square of each digit.

:param number: The number to check for happiness.
:return: True if the number is a happy number, False otherwise.

>>> is_happy_number(19)
True
>>> is_happy_number(2)
False
>>> is_happy_number(23)
True
>>> is_happy_number(1)
True
>>> is_happy_number(0)
Traceback (most recent call last):
...
ValueError: number=0 must be a positive integer
>>> is_happy_number(-19)
Traceback (most recent call last):
...
ValueError: number=-19 must be a positive integer
>>> is_happy_number(19.1)
Traceback (most recent call last):
...
ValueError: number=19.1 must be a positive integer
>>> is_happy_number("happy")
Traceback (most recent call last):
...
ValueError: number='happy' must be a positive integer
"""
if not isinstance(number, int) or number <= 0:
msg = f"{number=} must be a positive integer"
raise ValueError(msg)

seen = set()
while number != 1 and number not in seen:
seen.add(number)
number = sum(int(digit) ** 2 for digit in str(number))
return number == 1


if __name__ == "__main__":
import doctest

doctest.testmod()