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Commit 859ec51

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Doubly linked list in Python
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‎linked-list/double-linked-list.py

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# Copyright (C) Deepali Srivastava - All Rights Reserved
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# This code is part of DSA course available on CourseGalaxy.com
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class Node(object):
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def __init__(self,value):
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self.info = value
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self.prev = None
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self.next = None
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class DoubleLinkedList(object):
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def __init__(self):
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self.start = None
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def display_list(self):
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if self.start is None:
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print("List is empty")
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return
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print("List is : ")
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p = self.start
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while p is not None:
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print(p.info, " ", end='')
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p = p.next
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print()
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def insert_in_beginning(self,data):
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temp = Node(data)
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temp.next = self.start
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self.start.prev = temp
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self.start = temp
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def insert_in_empty_list(self,data):
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temp = Node(data)
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self.start = temp
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def insert_at_end(self,data):
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temp = Node(data)
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p = self.start
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while p.next is not None:
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p = p.next
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p.next = temp
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temp.prev = p
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def create_list(self):
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n = int(input("Enter the number of nodes : "))
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if n == 0:
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return
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data = int(input("Enter the first element to be inserted : "))
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self.insert_in_empty_list(data)
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for i in range(n-1):
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data = int(input("Enter the next element to be inserted : "))
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self.insert_at_end(data)
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def insert_after(self,data, x):
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temp = Node(data)
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p = self.start
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while p is not None:
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if p.info == x:
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break
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p = p.next
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if p is None:
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print(x," not present in the list")
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else:
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temp.prev = p
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temp.next = p.next
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if p.next is not None:
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p.next.prev = temp # should not be done when p refers to last node
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p.next = temp;
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def insert_before(self,data,x):
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if self.start is None:
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print("List is empty")
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return
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if self.start.info == x:
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temp = Node(data)
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temp.next = self.start
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self.start.prev = temp
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self.start = temp
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return
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p = self.start;
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while p is not None:
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if p.info == x:
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break
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p = p.next
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if p is None:
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print(x, " not present in the list")
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else:
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temp = Node(data)
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temp.prev = p.prev
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temp.next = p
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p.prev.next = temp
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p.prev = temp
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def delete_first_node(self):
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if self.start is None: # list is empty
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return
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if self.start.next is None: # list has only one node
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self.start = None
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return
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self.start = self.start.next
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self.start.prev = None
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def delete_last_node(self):
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if self.start is None: # list is empty
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return
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if self.start.next is None: # list has only one node
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self.start = None
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return
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p = self.start;
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while p.next != None:
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p = p.next;
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p.prev.next = None
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def delete_node(self,x):
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if self.start is None: # list is empty
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return
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if self.start.next is None: # list has only one node
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if self.start.info == x:
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self.start = None;
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else:
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print(x," not found")
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return
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# Deletion of first node
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if self.start.info == x:
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self.start = self.start.next
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self.start.prev = None
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return
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p = self.start.next
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while p.next is not None:
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if p.info == x:
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break
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p = p.next
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if p.next is not None : # node to be deleted is in between
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p.prev.next = p.next
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p.next.prev = p.prev;
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else: # p refers to last node
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if p.info == x: # node to be deleted is last node
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p.prev.next = None
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else:
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print(x," not found")
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def reverse_list(self):
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if self.start is None:
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return
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p1 = self.start
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p2 = p1.next
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p1.next = None
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p1.prev = p2
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while p2 is not None:
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p2.prev = p2.next
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p2.next = p1
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p1 = p2
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p2 = p2.prev
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self.start = p1
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#########################################################################
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list = DoubleLinkedList()
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list.create_list()
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while True:
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print("1.Display list")
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print("2.Insert in empty list")
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print("3.Insert a node in the beginning of the list")
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print("4.Insert a node at the end of the list")
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print("5.Insert a node after a specified node")
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print("6.Insert a node before a specified node")
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print("7.Delete first node")
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print("8.Delete last node")
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print("9.Delete any node")
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print("10.Reverse the list")
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print("11.Quit")
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option = int(input("Enter your choice : " ))
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if option == 1:
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list.display_list()
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elif option == 2:
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data = int(input("Enter the element to be inserted : "))
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list.insert_in_empty_list(data)
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elif option == 3:
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data = int(input("Enter the element to be inserted : "))
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list.insert_in_beginning(data)
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elif option == 4:
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data = int(input("Enter the element to be inserted : "))
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list.insert_at_end(data)
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elif option == 5:
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data = int(input("Enter the element to be inserted : "))
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x = int(input("Enter the element after which to insert : "))
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list.insert_after(data,x)
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elif option == 6:
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data = int(input("Enter the element to be inserted : "))
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x = int(input("Enter the element before which to insert : "))
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list.insert_before(data,x)
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elif option == 7:
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list.delete_first_node()
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elif option == 8:
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list.delete_last_node()
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elif option == 9:
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data = int(input("Enter the element to be deleted : "))
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list.delete_node(data)
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elif option == 10:
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list.reverse_list()
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elif option == 11:
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break
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else:
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print("Wrong option")
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print()
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