Question

我正在尝试编写一个程序，它将打印给定范围内的所有素数。我写了它，输出几乎没问题，它打印素数，但由于某种原因它打印4，这不是一个主要的... 任何助理都将非常感激！

def primes():
    start = int(input("Enter the starting number: "))
    end = int(input("Enter the ending number: "))
    num = 0
    i = 0
    ctr = 0
    for num in range(start,end+1,1):
        ctr = 0
        for i in range(2,num//2,1):
            if num % i == 0 :
                ctr = ctr + 1
                break
        if (ctr==0 and num != 1):
            print(num)

Answer 1

for i in range(2,num//2,1):

让我们在num = 4时检查这段代码，它变为

for i in range(2,2,1):

现在我们看到了问题。溶液..？

for i in range(2,(num//2)+1,1):

Answer 2

以下方法都是可能用于在您的范围内检查的素数检查器：

def isPrime(Number):  # slow
    return 2 in [Number, 2 ** Number % Number]


def isprime(n):  # out of memory errors with big numbers
    """check if integer n is a prime"""
    # make sure n is a positive integer
    n = abs(int(n))
    # 0 and 1 are not primes
    if n < 2:
        return False
    # 2 is the only even prime number
    if n == 2:
        return True
        # all other even numbers are not primes
    if not n & 1:
        return False
    # range starts with 3 and only needs to go up the squareroot of n
    # for all odd numbers
    for x in range(3, int(n ** 0.5) + 1, 2):
        if n % x == 0:
            return False
    return True


def is_prime(n):  # Best until now
    if n == 2 or n == 3:
        return True
    if n < 2 or n % 2 == 0:
        return False
    if n < 9:
        return True
    if n % 3 == 0:
        return False
    r = int(n ** 0.5)
    f = 5
    while f <= r:
        # print '\t', f
        if n % f == 0:
            return False
        if n % (f + 2) == 0:
            return False
        f += 6
    return True

Answer 3

MATCH (u:NodeType)
WITH u
ORDER BY u.Y DESC
WITH u.X AS X, collect(u) AS us
RETURN us[0] AS u

以上是错误的。您正在从for i in range(2,num//2,1):迭代到2 您应该从num / 2 - 1迭代到2。（sqrt(num)）
或者，您可以对range(2, int(math.sqrt(n)) + 1)进行特殊检查，并将范围修改为2

一个范围内的所有素数

3 个答案: