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* actions/checkout@v2 https://github.com/actions/checkout/releases * fixup! Format Python code with psf/black push
124 lines
2.9 KiB
Python
124 lines
2.9 KiB
Python
# A complete working Python program to demonstrate all
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# stack operations using a doubly linked list
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class Node:
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def __init__(self, data):
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self.data = data # Assign data
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self.next = None # Initialize next as null
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self.prev = None # Initialize prev as null
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class Stack:
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"""
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>>> stack = Stack()
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>>> stack.is_empty()
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True
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>>> stack.print_stack()
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stack elements are:
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>>> for i in range(4):
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... stack.push(i)
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...
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>>> stack.is_empty()
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False
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>>> stack.print_stack()
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stack elements are:
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3->2->1->0->
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>>> stack.top()
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3
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>>> len(stack)
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4
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>>> stack.pop()
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3
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>>> stack.print_stack()
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stack elements are:
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2->1->0->
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"""
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def __init__(self):
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self.head = None
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def push(self, data):
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"""add a Node to the stack"""
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if self.head is None:
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self.head = Node(data)
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else:
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new_node = Node(data)
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self.head.prev = new_node
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new_node.next = self.head
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new_node.prev = None
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self.head = new_node
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def pop(self):
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"""pop the top element off the stack"""
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if self.head is None:
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return None
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else:
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temp = self.head.data
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self.head = self.head.next
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self.head.prev = None
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return temp
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def top(self):
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"""return the top element of the stack"""
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return self.head.data
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def __len__(self):
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temp = self.head
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count = 0
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while temp is not None:
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count += 1
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temp = temp.next
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return count
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def is_empty(self):
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return self.head is None
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def print_stack(self):
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print("stack elements are:")
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temp = self.head
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while temp is not None:
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print(temp.data, end="->")
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temp = temp.next
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# Code execution starts here
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if __name__ == "__main__":
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# Start with the empty stack
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stack = Stack()
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# Insert 4 at the beginning. So stack becomes 4->None
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print("Stack operations using Doubly LinkedList")
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stack.push(4)
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# Insert 5 at the beginning. So stack becomes 4->5->None
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stack.push(5)
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# Insert 6 at the beginning. So stack becomes 4->5->6->None
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stack.push(6)
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# Insert 7 at the beginning. So stack becomes 4->5->6->7->None
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stack.push(7)
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# Print the stack
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stack.print_stack()
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# Print the top element
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print("\nTop element is ", stack.top())
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# Print the stack size
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print("Size of the stack is ", len(stack))
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# pop the top element
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stack.pop()
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# pop the top element
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stack.pop()
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# two elements have now been popped off
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stack.print_stack()
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# Print True if the stack is empty else False
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print("\nstack is empty:", stack.is_empty())
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