diff --git a/DIRECTORY.md b/DIRECTORY.md index 866e0d658bf660c9c65bc826a368a7b2090d4483..f0f494e7a3b41aaf046c97ffa71bcbd255341d7d 100644 --- a/DIRECTORY.md +++ b/DIRECTORY.md @@ -671,6 +671,8 @@ * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_062/sol1.py) * Problem 063 * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_063/sol1.py) + * Problem 065 + * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_065/sol1.py) * Problem 067 * [Sol1](https://github.com/TheAlgorithms/Python/blob/master/project_euler/problem_067/sol1.py) * Problem 069 diff --git a/project_euler/problem_065/__init__.py b/project_euler/problem_065/__init__.py new file mode 100644 index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391 diff --git a/project_euler/problem_065/sol1.py b/project_euler/problem_065/sol1.py new file mode 100644 index 0000000000000000000000000000000000000000..229769a77d07f0845a0c55f398a348d13956f2c2 --- /dev/null +++ b/project_euler/problem_065/sol1.py @@ -0,0 +1,99 @@ +""" +Project Euler Problem 65: https://projecteuler.net/problem=65 + +The square root of 2 can be written as an infinite continued fraction. + +sqrt(2) = 1 + 1 / (2 + 1 / (2 + 1 / (2 + 1 / (2 + ...)))) + +The infinite continued fraction can be written, sqrt(2) = [1;(2)], (2) +indicates that 2 repeats ad infinitum. In a similar way, sqrt(23) = +[4;(1,3,1,8)]. + +It turns out that the sequence of partial values of continued +fractions for square roots provide the best rational approximations. +Let us consider the convergents for sqrt(2). + +1 + 1 / 2 = 3/2 +1 + 1 / (2 + 1 / 2) = 7/5 +1 + 1 / (2 + 1 / (2 + 1 / 2)) = 17/12 +1 + 1 / (2 + 1 / (2 + 1 / (2 + 1 / 2))) = 41/29 + +Hence the sequence of the first ten convergents for sqrt(2) are: +1, 3/2, 7/5, 17/12, 41/29, 99/70, 239/169, 577/408, 1393/985, 3363/2378, ... + +What is most surprising is that the important mathematical constant, +e = [2;1,2,1,1,4,1,1,6,1,...,1,2k,1,...]. + +The first ten terms in the sequence of convergents for e are: +2, 3, 8/3, 11/4, 19/7, 87/32, 106/39, 193/71, 1264/465, 1457/536, ... + +The sum of digits in the numerator of the 10th convergent is +1 + 4 + 5 + 7 = 17. + +Find the sum of the digits in the numerator of the 100th convergent +of the continued fraction for e. + +----- + +The solution mostly comes down to finding an equation that will generate +the numerator of the continued fraction. For the i-th numerator, the +pattern is: + +n_i = m_i * n_(i-1) + n_(i-2) + +for m_i = the i-th index of the continued fraction representation of e, +n_0 = 1, and n_1 = 2 as the first 2 numbers of the representation. + +For example: +n_9 = 6 * 193 + 106 = 1264 +1 + 2 + 6 + 4 = 13 + +n_10 = 1 * 193 + 1264 = 1457 +1 + 4 + 5 + 7 = 17 +""" + + +def sum_digits(num: int) -> int: + """ + Returns the sum of every digit in num. + + >>> sum_digits(1) + 1 + >>> sum_digits(12345) + 15 + >>> sum_digits(999001) + 28 + """ + digit_sum = 0 + while num > 0: + digit_sum += num % 10 + num //= 10 + return digit_sum + + +def solution(max: int = 100) -> int: + """ + Returns the sum of the digits in the numerator of the max-th convergent of + the continued fraction for e. + + >>> solution(9) + 13 + >>> solution(10) + 17 + >>> solution(50) + 91 + """ + pre_numerator = 1 + cur_numerator = 2 + + for i in range(2, max + 1): + temp = pre_numerator + e_cont = 2 * i // 3 if i % 3 == 0 else 1 + pre_numerator = cur_numerator + cur_numerator = e_cont * pre_numerator + temp + + return sum_digits(cur_numerator) + + +if __name__ == "__main__": + print(f"{solution() = }")