Python/project_euler/problem_112/sol1.py
2021-10-06 22:11:50 +08:00

92 lines
2.7 KiB
Python

"""
Problem 112: https://projecteuler.net/problem=112
Working from left-to-right if no digit is exceeded by the digit to its left it is
called an increasing number; for example, 134468.
Similarly if no digit is exceeded by the digit to its right it is called a decreasing
number; for example, 66420.
We shall call a positive integer that is neither increasing nor decreasing a "bouncy"
number, for example, 155349.
Clearly there cannot be any bouncy numbers below one-hundred, but just over half of
the numbers below one-thousand (525) are bouncy. In fact, the least number for which
the proportion of bouncy numbers first reaches 50% is 538.
Surprisingly, bouncy numbers become more and more common and by the time we reach
21780 the proportion of bouncy numbers is equal to 90%.
Find the least number for which the proportion of bouncy numbers is exactly 99%.
"""
def check_bouncy(n: int) -> bool:
"""
Returns True if number is bouncy, False otherwise
>>> check_bouncy(6789)
False
>>> check_bouncy(-12345)
False
>>> check_bouncy(0)
False
>>> check_bouncy(6.74)
Traceback (most recent call last):
...
ValueError: check_bouncy() accepts only integer arguments
>>> check_bouncy(132475)
True
>>> check_bouncy(34)
False
>>> check_bouncy(341)
True
>>> check_bouncy(47)
False
>>> check_bouncy(-12.54)
Traceback (most recent call last):
...
ValueError: check_bouncy() accepts only integer arguments
>>> check_bouncy(-6548)
True
"""
if not isinstance(n, int):
raise ValueError("check_bouncy() accepts only integer arguments")
str_n = str(n)
sorted_str_n = "".join(sorted(str_n))
return sorted_str_n != str_n and sorted_str_n[::-1] != str_n
def solution(percent: float = 99) -> int:
"""
Returns the least number for which the proportion of bouncy numbers is
exactly 'percent'
>>> solution(50)
538
>>> solution(90)
21780
>>> solution(80)
4770
>>> solution(105)
Traceback (most recent call last):
...
ValueError: solution() only accepts values from 0 to 100
>>> solution(100.011)
Traceback (most recent call last):
...
ValueError: solution() only accepts values from 0 to 100
"""
if not 0 < percent < 100:
raise ValueError("solution() only accepts values from 0 to 100")
bouncy_num = 0
num = 1
while True:
if check_bouncy(num):
bouncy_num += 1
if (bouncy_num / num) * 100 >= percent:
return num
num += 1
if __name__ == "__main__":
from doctest import testmod
testmod()
print(f"{solution(99)}")