2. Stack using Linked List

In [1]:

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

    def __repr__(self):
        return "<Node: %s>" % self.data

class Node: def __init__(self, data): self.data = data self.next = None def __repr__(self): return "" % self.data

In [2]:

Node(10)

Node(10)

Out[2]:

<Node: 10>

In [3]:

class StackUsingLinkedList:
    def __init__(self):
        self.__top = -1
        self.head = None

    def __repr__(self):
        current = self.head
        nodes = []
        while current != None:
            if current == self.head:
                nodes.append("[Top: %s]" % current.data)
            else:
                nodes.append("[%s]" % current.data)
            current = current.next

        return ", ".join(nodes)

    def __iter__(self):
        current = self.head
        while current:
            yield current.data
            current = current.next

    def __len__(self):
        return self.__top + 1

    def is_empty(self):
        return self.head == None and self.__top == -1

    def peek(self):
        if self.is_empty():
            print("Stack is empty, nothing to peek()")
        else:
            print("Element at top is: {}".format(self.head))
            # return "<Element: %s>" % self.head.data
            return self.head

    def push(self, data):
        node = Node(data)
        if self.head == None:
            print("Inserting first element: {}".format(data))
            self.head = node
        else:
            print("Inserting another element: {}".format(data))
            node.next = self.head
            self.head = node
        self.__top += 1

    def pop(self):
        if self.__top == -1 or self.head == None:
            print("Stack is empty, nothing to pop()")
            return

        current = self.head
        if current.next == None:
            print("at last element")
            self.head = None
        else:
            self.head = current.next

        data = current.data
        del current
        self.__top -= 1
        return data

class StackUsingLinkedList: def __init__(self): self.__top = -1 self.head = None def __repr__(self): current = self.head nodes = [] while current != None: if current == self.head: nodes.append("[Top: %s]" % current.data) else: nodes.append("[%s]" % current.data) current = current.next return ", ".join(nodes) def __iter__(self): current = self.head while current: yield current.data current = current.next def __len__(self): return self.__top + 1 def is_empty(self): return self.head == None and self.__top == -1 def peek(self): if self.is_empty(): print("Stack is empty, nothing to peek()") else: print("Element at top is: {}".format(self.head)) # return "" % self.head.data return self.head def push(self, data): node = Node(data) if self.head == None: print("Inserting first element: {}".format(data)) self.head = node else: print("Inserting another element: {}".format(data)) node.next = self.head self.head = node self.__top += 1 def pop(self): if self.__top == -1 or self.head == None: print("Stack is empty, nothing to pop()") return current = self.head if current.next == None: print("at last element") self.head = None else: self.head = current.next data = current.data del current self.__top -= 1 return data

In [4]:

stack = StackUsingLinkedList()

stack = StackUsingLinkedList()

In [5]:

for i in range(0, 6):
    stack.push(i)

for i in range(0, 6): stack.push(i)

Inserting first element: 0
Inserting another element: 1
Inserting another element: 2
Inserting another element: 3
Inserting another element: 4
Inserting another element: 5

In [6]:

stack

stack

Out[6]:

[Top: 5], [4], [3], [2], [1], [0]

In [7]:

len(stack)

len(stack)

Out[7]:

6

In [8]:

for i in stack:
    print(i)

for i in stack: print(i)

5
4
3
2
1
0

In [9]:

stack.is_empty()

stack.is_empty()

Out[9]:

False

In [10]:

stack.peek()

stack.peek()

Element at top is: <Node: 5>

Out[10]:

<Node: 5>

In [11]:

for _ in range(0, 7):
    stack.pop()

for _ in range(0, 7): stack.pop()

at last element
Stack is empty, nothing to pop()

In [12]:

stack

stack

Out[12]:

In [13]:

stack.pop()

stack.pop()

Stack is empty, nothing to pop()

In [ ]: