|
| 1 | +""" |
| 2 | +Project Euler Problem 800: https://projecteuler.net/problem=800 |
| 3 | +
|
| 4 | +An integer of the form p^q q^p with prime numbers p != q is called a hybrid-integer. |
| 5 | +For example, 800 = 2^5 5^2 is a hybrid-integer. |
| 6 | +
|
| 7 | +We define C(n) to be the number of hybrid-integers less than or equal to n. |
| 8 | +You are given C(800) = 2 and C(800^800) = 10790 |
| 9 | +
|
| 10 | +Find C(800800^800800) |
| 11 | +""" |
| 12 | + |
| 13 | +from math import isqrt, log2 |
| 14 | + |
| 15 | + |
| 16 | +def calculate_prime_numbers(max_number: int) -> list[int]: |
| 17 | + """ |
| 18 | + Returns prime numbers below max_number |
| 19 | +
|
| 20 | + >>> calculate_prime_numbers(10) |
| 21 | + [2, 3, 5, 7] |
| 22 | + """ |
| 23 | + |
| 24 | + is_prime = [True] * max_number |
| 25 | + for i in range(2, isqrt(max_number - 1) + 1): |
| 26 | + if is_prime[i]: |
| 27 | + for j in range(i**2, max_number, i): |
| 28 | + is_prime[j] = False |
| 29 | + |
| 30 | + return [i for i in range(2, max_number) if is_prime[i]] |
| 31 | + |
| 32 | + |
| 33 | +def solution(base: int = 800800, degree: int = 800800) -> int: |
| 34 | + """ |
| 35 | + Returns the number of hybrid-integers less than or equal to base^degree |
| 36 | +
|
| 37 | + >>> solution(800, 1) |
| 38 | + 2 |
| 39 | +
|
| 40 | + >>> solution(800, 800) |
| 41 | + 10790 |
| 42 | + """ |
| 43 | + |
| 44 | + upper_bound = degree * log2(base) |
| 45 | + max_prime = int(upper_bound) |
| 46 | + prime_numbers = calculate_prime_numbers(max_prime) |
| 47 | + |
| 48 | + hybrid_integers_count = 0 |
| 49 | + left = 0 |
| 50 | + right = len(prime_numbers) - 1 |
| 51 | + while left < right: |
| 52 | + while ( |
| 53 | + prime_numbers[right] * log2(prime_numbers[left]) |
| 54 | + + prime_numbers[left] * log2(prime_numbers[right]) |
| 55 | + > upper_bound |
| 56 | + ): |
| 57 | + right -= 1 |
| 58 | + hybrid_integers_count += right - left |
| 59 | + left += 1 |
| 60 | + |
| 61 | + return hybrid_integers_count |
| 62 | + |
| 63 | + |
| 64 | +if __name__ == "__main__": |
| 65 | + print(f"{solution() = }") |
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