Python/project_euler/problem_180/sol1.py

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"""
Project Euler Problem 234: https://projecteuler.net/problem=234
For any integer n, consider the three functions
f1,n(x,y,z) = x^(n+1) + y^(n+1) - z^(n+1)
f2,n(x,y,z) = (xy + yz + zx)*(x^(n-1) + y^(n-1) - z^(n-1))
f3,n(x,y,z) = xyz*(xn-2 + yn-2 - zn-2)
and their combination
fn(x,y,z) = f1,n(x,y,z) + f2,n(x,y,z) - f3,n(x,y,z)
We call (x,y,z) a golden triple of order k if x, y, and z are all rational numbers
of the form a / b with 0 < a < b k and there is (at least) one integer n,
so that fn(x,y,z) = 0.
Let s(x,y,z) = x + y + z.
Let t = u / v be the sum of all distinct s(x,y,z) for all golden triples
(x,y,z) of order 35.
All the s(x,y,z) and t must be in reduced form.
Find u + v.
Solution:
By expanding the brackets it is easy to show that
fn(x, y, z) = (x + y + z) * (x^n + y^n - z^n).
Since x,y,z are positive, the requirement fn(x, y, z) = 0 is fulfilled if and
only if x^n + y^n = z^n.
By Fermat's Last Theorem, this means that the absolute value of n can not
exceed 2, i.e. n is in {-2, -1, 0, 1, 2}. We can eliminate n = 0 since then the
equation would reduce to 1 + 1 = 1, for which there are no solutions.
So all we have to do is iterate through the possible numerators and denominators
of x and y, calculate the corresponding z, and check if the corresponding numerator and
denominator are integer and satisfy 0 < z_num < z_den <= 0. We use a set "uniquq_s"
to make sure there are no duplicates, and the fractions.Fraction class to make sure
we get the right numerator and denominator.
Reference:
https://en.wikipedia.org/wiki/Fermat%27s_Last_Theorem
"""
from fractions import Fraction
from math import gcd, sqrt
from typing import Tuple
def is_sq(number: int) -> bool:
"""
Check if number is a perfect square.
>>> is_sq(1)
True
>>> is_sq(1000001)
False
>>> is_sq(1000000)
True
"""
sq: int = int(number ** 0.5)
return number == sq * sq
def add_three(
x_num: int, x_den: int, y_num: int, y_den: int, z_num: int, z_den: int
) -> Tuple[int, int]:
"""
Given the numerators and denominators of three fractions, return the
numerator and denominator of their sum in lowest form.
>>> add_three(1, 3, 1, 3, 1, 3)
(1, 1)
>>> add_three(2, 5, 4, 11, 12, 3)
(262, 55)
"""
top: int = x_num * y_den * z_den + y_num * x_den * z_den + z_num * x_den * y_den
bottom: int = x_den * y_den * z_den
hcf: int = gcd(top, bottom)
top //= hcf
bottom //= hcf
return top, bottom
def solution(order: int = 35) -> int:
"""
Find the sum of the numerator and denominator of the sum of all s(x,y,z) for
golden triples (x,y,z) of the given order.
>>> solution(5)
296
>>> solution(10)
12519
>>> solution(20)
19408891927
"""
unique_s: set = set()
hcf: int
total: Fraction = Fraction(0)
fraction_sum: Tuple[int, int]
for x_num in range(1, order + 1):
for x_den in range(x_num + 1, order + 1):
for y_num in range(1, order + 1):
for y_den in range(y_num + 1, order + 1):
# n=1
z_num = x_num * y_den + x_den * y_num
z_den = x_den * y_den
hcf = gcd(z_num, z_den)
z_num //= hcf
z_den //= hcf
if 0 < z_num < z_den <= order:
fraction_sum = add_three(
x_num, x_den, y_num, y_den, z_num, z_den
)
unique_s.add(fraction_sum)
# n=2
z_num = (
x_num * x_num * y_den * y_den + x_den * x_den * y_num * y_num
)
z_den = x_den * x_den * y_den * y_den
if is_sq(z_num) and is_sq(z_den):
z_num = int(sqrt(z_num))
z_den = int(sqrt(z_den))
hcf = gcd(z_num, z_den)
z_num //= hcf
z_den //= hcf
if 0 < z_num < z_den <= order:
fraction_sum = add_three(
x_num, x_den, y_num, y_den, z_num, z_den
)
unique_s.add(fraction_sum)
# n=-1
z_num = x_num * y_num
z_den = x_den * y_num + x_num * y_den
hcf = gcd(z_num, z_den)
z_num //= hcf
z_den //= hcf
if 0 < z_num < z_den <= order:
fraction_sum = add_three(
x_num, x_den, y_num, y_den, z_num, z_den
)
unique_s.add(fraction_sum)
# n=2
z_num = x_num * x_num * y_num * y_num
z_den = (
x_den * x_den * y_num * y_num + x_num * x_num * y_den * y_den
)
if is_sq(z_num) and is_sq(z_den):
z_num = int(sqrt(z_num))
z_den = int(sqrt(z_den))
hcf = gcd(z_num, z_den)
z_num //= hcf
z_den //= hcf
if 0 < z_num < z_den <= order:
fraction_sum = add_three(
x_num, x_den, y_num, y_den, z_num, z_den
)
unique_s.add(fraction_sum)
for num, den in unique_s:
total += Fraction(num, den)
return total.denominator + total.numerator
if __name__ == "__main__":
print(f"{solution() = }")