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84 lines
1.8 KiB
Python
84 lines
1.8 KiB
Python
"""
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Project Euler Problem 10: https://projecteuler.net/problem=10
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Summation of primes
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The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
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Find the sum of all the primes below two million.
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References:
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- https://en.wikipedia.org/wiki/Prime_number
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"""
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import math
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from collections.abc import Iterator
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from itertools import takewhile
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def is_prime(number: int) -> bool:
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"""Checks to see if a number is a prime in O(sqrt(n)).
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A number is prime if it has exactly two factors: 1 and itself.
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Returns boolean representing primality of given number num (i.e., if the
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result is true, then the number is indeed prime else it is not).
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>>> is_prime(2)
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True
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>>> is_prime(3)
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True
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>>> is_prime(27)
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False
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>>> is_prime(2999)
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True
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>>> is_prime(0)
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False
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>>> is_prime(1)
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False
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"""
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if 1 < number < 4:
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# 2 and 3 are primes
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return True
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elif number < 2 or number % 2 == 0 or number % 3 == 0:
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# Negatives, 0, 1, all even numbers, all multiples of 3 are not primes
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return False
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# All primes number are in format of 6k +/- 1
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for i in range(5, int(math.sqrt(number) + 1), 6):
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if number % i == 0 or number % (i + 2) == 0:
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return False
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return True
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def prime_generator() -> Iterator[int]:
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"""
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Generate a list sequence of prime numbers
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"""
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num = 2
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while True:
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if is_prime(num):
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yield num
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num += 1
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def solution(n: int = 2000000) -> int:
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"""
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Returns the sum of all the primes below n.
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>>> solution(1000)
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76127
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>>> solution(5000)
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1548136
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>>> solution(10000)
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5736396
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>>> solution(7)
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10
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"""
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return sum(takewhile(lambda x: x < n, prime_generator()))
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if __name__ == "__main__":
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print(f"{solution() = }")
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