常见题目

from math import sqrt


def fun(n):
    li = []
    for i in range(2, n + 1):
        count = 0
        for j in range(2, int(sqrt(i) + 1)):
            ‘‘‘
            不用除到n是因为：
            假如一个数N是合数,它有一个约数a,那么有a×b=N
            则a、b两个数中必有一个大于或等于根号N,一个小于或等于根号N。
            因此,只要小于或等于根号N的数（1除外）不能整除N,则N一定是素数
            ‘‘‘
            if i % j == 0:
                count += 1
        if count == 0:
            li.append(i)
    return li


def fun2(n):
    ‘‘‘
    5及以上的自然数可以表示为  6x+5 6x 6x +1 6x+2 6x+3 6x+4 其中只有6x+5和6x+1 不被2，3整除，所以有以下：
    ‘‘‘
    li = [2, 3]
    for i in range(5, n + 1):
        if i % 6 == 1 or i % 6 == 5:
            li.append(i)

    return li


print(fun(100))

print(fun(5))

class Node(object):
    def __init__(self, elem, next_=None):
        self.elem = elem
        self.next = next_
 
def reverseList(head):
    if head == None or head.next==None:  # 若链表为空或者仅一个数就直接返回
        return head 
    pre = None
    next = None
    while(head != None): 
        next = head.next     # 1
        head.next = pre     # 2
        pre = head      # 3
        head = next      # 4
    return pre

if __name__ == ‘__main__‘:
    l1 = Node(3)    # 建立链表3->2->1->9->None
    l1.next = Node(2)
    l1.next.next = Node(1)
    l1.next.next.next = Node(9)
    l = reverseList(l1)
    print (l.elem, l.next.elem, l.next.next.elem, l.next.next.next.elem)