漏印行

Question

我正在尝试打印程序，因此它看起来像这样。

插入 1
插入 2
插入 3
顶部元素是 3
删除 3
删除 2
删除 1
堆栈为空

但是当我运行程序时，我错过了“插入1”。我的代码看起来像这样

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

    def isempty(self):
        if self.head == None:
            return True
        else:
            return False

    def push(self,data):
        if self.head == None:
            self.head=Node(data)
        else:
            newnode = Node(data)
            newnode.next = self.head
            self.head = newnode
            print("Inserting ", str(self.head.data))
    
    def pop(self):
        if self.isempty():
            return None
        else:
            poppednode = self.head
            self.head = self.head.next
            poppednode.next = None
            print("Removing",poppednode.data)
            return poppednode.data

    def peek(self):
        if self.isempty():
            return None
        else:
            return self.head.data

    def display(self):
        iternode = self.head
        if self.isempty():
            print("The stack is empty")
        else:
            while(iternode != None):
                print(iternode.data,"->",end = "")
                iternode = iternode.next
            return
        
stack = Stack()
stack.push(1)
stack.push(2)
stack.push(3)

print("Top element is ",stack.peek())

stack.pop()
stack.pop()
stack.pop()
stack.display()

Answer 1

当你第一次按下时 self.head 将是 None 并且它不会进入打印“插入 1”的其他条件

Answer 2

第一次推送项目时，self.head 是 None，所以第一个代码块被执行。取消缩进 print('Insert') 行，以便在两种情况下打印。

    def push(self,data):
        if self.head == None:
            self.head = Node(data)
        else:
            newnode = Node(data)
            newnode.next = self.head
            self.head = newnode
        print("Inserting ", str(self.head.data)) # <== unindent 1-level

漏印行

Missed Print Line

python

stack

linked-list

data-structures

singly-linked-list