如何在不使用 for 或 while 循环的情况下浏览链接列表？

Question

我试图在不使用 for 循环或 while 循环的情况下遍历链表。

class VaccList:
    class Appointment:
        def __init__(self, name, age, city, date):
            assert type(name) is str, 'name variable must be a string'
            assert type(age) is int, 'age variable must be a integer'
            assert type(city) is str, 'city variable must be a string'
            assert type(date) is datetime, 'date variable must be a datetime object'
            assert name != None, 'name variable cannot be empty'
            assert age >= 18 and age <= 100, 'age must be between 18 and 100'
            #   ADD 6 asserts.  4 for the types and name cannot be empty, 
            #   and age must be between 18 and 100

            self.name = name
            self.age = age
            self.city = city
            self.date = date
            self.confirmed = False
            self.next = None

        def __str__(self):
            s = "Appointment for " + self.name + " on " + str(self.date) + " age:" + str(self.age) + "  city:" + self.city
            if self.confirmed:
                s += " (confirmed)"
            else:
                s += " (unconfirmed)"
            return s

    def __init__(self):
        self.head = None
        self.tail = None


    def confirm(self, name):    
        '''
        Find an appointment for a person with the given name and set confirmed to true.
        Return a string message  "not found", "confirmed", "already confirmed."
    '''
        # Note... no loop!
        #  assert, type of name and non-empty string
        assert type(name) is str, 'name variable must be a string'
        assert name != None
        current = self.head
        if current.name == name:
            if current.confirmed == False:
                current.confirmed = True
                return 'confirmed'
            else:
                return 'already confirmed'

这是我创建的课程中的方法，我正在尝试确认约会，除非它们已经被确认。我可以确认第一次约会，但如果我正在搜索的姓名不是约会列表中的第一个名字，我将如何找到下一个要检查的名字？

Answer 1

下面是如何按照@user15270287 早期建议的那样递归地执行操作来避免循环。我必须添加一个 add_appt() 方法才能将它们添加到列表中，以便能够创建一个用于测试代码，因此您的里程可能会有所不同。

除此之外和最后的单元测试，所有的变化都是confirm()方法。

from datetime import datetime


class VaccList:
    class Appointment:
        def __init__(self, name, age, city, date):
            assert type(name) is str, 'name variable must be a string'
            assert type(age) is int, 'age variable must be a integer'
            assert type(city) is str, 'city variable must be a string'
            assert type(date) is datetime, 'date variable must be a datetime object'
            assert name != None, 'name variable cannot be empty'
            assert age >= 18 and age <= 100, 'age must be between 18 and 100'
            #   ADD 6 asserts.  4 for the types and name cannot be empty,
            #   and age must be between 18 and 100

            self.name = name
            self.age = age
            self.city = city
            self.date = date
            self.confirmed = False
            self.next = None

        def __str__(self):
            s = ("Appointment for " + self.name + " on " + str(self.date) + " age:"
                    + str(self.age) + "  city:" + self.city)
            if self.confirmed:
                s += " (confirmed)"
            else:
                s += " (unconfirmed)"
            return s

    def __init__(self):
        self.head = None
        self.tail = None

    # ADDED FOR TESTING PURPOSES.
    def add_appt(self, name, age, city, date):
        date = datetime.strptime(date, '%Y-%m-%d')
        new_appt = VaccList.Appointment(name, age, city, date)
        new_appt.next = self.head
        self.head = new_appt

    def confirm(self, name, start=None):
        '''
        Find an appointment for a person with the given name and set confirmed to true.
        Return a string message  "not found", "confirmed", "already confirmed."
        '''
        # Note... no loop!
        #  assert, type of name and non-empty string
        assert type(name) is str, 'name variable must be a string'
        assert name != None

        # Start at beginning of list unless different node is specified.
        current = self.head if start is None else start
        if current is None:
            return 'list is empty!'
        if current.name == name:
            if current.confirmed == False:
                current.confirmed = True
                return 'confirmed'
            else:
                return 'already confirmed'
        else:
            if current.next is None:  # End of list?
                return 'not found'
            return self.confirm(name, start=current.next)


if __name__ == '__main__':

    vlist = VaccList()
    vlist.add_appt('Bob', 25, 'Tacoma', '2021-03-21')
    vlist.add_appt('Sue', 31, 'Seattle', '2021-03-22')
    vlist.add_appt('Ted', 28, 'Auburn', '2021-03-23')

    result = vlist.confirm('Sue')
    print('Sue is {}'.format(result))
    result = vlist.confirm('Sue')
    print('Sue is now {}'.format(result))