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49 lines
1.5 KiB
Python
49 lines
1.5 KiB
Python
'''Python program to print all Primes Smaller than or equal to N using Sieve of Eratosthenes'''
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import time
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import math
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def sieve_of_eratosthenes(num: int) -> list[int]:
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"""Finds all prime number from 1 to num.
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Args:
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num (int): Number up to which the prime numbers should be printed
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Returns:
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list[int]: List of prime numbers
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"""
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# boolean list to store if a number is prime or not
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prime = [True] * (num+1)
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p = 2 # starting prime number
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# we will iterate till square root of num because
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# if a number is not prime then it will have a factor less than or equal to square root of that number
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while p <= math.sqrt(num):
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# If prime[p] is not
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# changed, then it is a prime
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if prime[p]:
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i = (p << 1) # i = p * 2
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# Updating all multiples of p
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while i <= num:
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prime[i] = False
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i += p
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p += 1
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return [p for p in range(2, num+1) if prime[p]]
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def print_sieve(num: int) -> None:
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"""Prints all prime number from 1 to num.
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Args:
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num (int): Number up to which the prime numbers should be printed
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"""
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for number in sieve_of_eratosthenes(num):
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print(number, end=" ")
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# Driver code
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if __name__ == '__main__':
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num = int(input("Enter a number: "))
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while num < 2:
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print("Limit smaller than 2, pick another number")
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num = int(input("Enter a number: "))
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print(f"Following are the prime numbers smaller than or equal to {num}")
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print_sieve(num) |