链接列表中特定事件的计数器

Question

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

head = Node("Cat")
another_node = Node("Dog")
head.next = another_node
a_third_node = Node("Bird")
another_node.next = a_third_node
last_node = Node("Dog")
a_third_node.next = last_node

node = head   # copy the address of the head node into node
while node != None:
    print ("List item: ", node.data)
    node = node.next

对于上面的代码，我得到以下输出：

>>> 
List item:  Cat
List item:  Dog
List item:  Bird
List item:  Dog
>>>

我需要在此程序中包含一种计算列表中特定数据的次数的方法。那么我怎样才能创建一个显示＆＃34; Dog＆＃34;在列表中两次？

Answer 1

你快到了。只要看到给定value而不是仅打印数据，只需递增计数器变量：

def count(head, value):
    seen = 0
    while head is not None:
        if head.data == value:
            seen += 1
        head = head.next
    return seen

#...
print(count(head, "Dog"))