Python program to search an element in a doubly linked list.

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Python program to search an element in a doubly linked list.

In this program, we need to search a given node in a doubly linked list.

Python program to search an element in a doubly linked list

To solve this problem, we will traverse through the list using a node current. Current points to head and start comparing searched node data with current node data. If they are equal, set the flag to true and print the message along with the position of the searched node.

For eg., In above list, a search node says 4 can be found at the position 3.

ALGORITHM:

  1. Define a Node class which represents a node in the list. It will have three properties: data, previous which will point to the previous node and next which will point to the next node.
  2. Define another class for creating a doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
  3. addNode() will add node to the list:
  • It first checks whether the head is null, then it will insert the node as the head.
  • Both head and tail will point to a newly added node.
  • Head’s previous pointer will point to null and tail’s next pointer will point to null.
  • If the head is not null, the new node will be inserted at the end of the list such that new node’s previous pointer will point to tail.
  • The new node will become the new tail. Tail’s next pointer will point to null.

a. searchNode() will search for a node in the list:

  • Variable i will keep track of the position of the searched node.
  • The variable flag will store boolean value false.
  • Current will point to head node.
  • Iterate through the loop by incrementing current to current.next and i to i + 1.
  • Compare each node’s data with the searched node if a match is found, set the flag to true.
  • If the flag is true, prints the position of the searched node.
  • Else, print the message “Element is not present in the list”.

PROGRAM:

  1. #Represent a node of doubly linked list  
  2. class Node:
  3.     def __init__(self,data):
  4.         self.data = data;
  5.         self.previous = None;
  6.         self.next = None;
  7. class SearchList:
  8.     #Represent the head and tail of the doubly linked list  
  9.     def __init__(self):
  10.         self.head = None;
  11.         self.tail = None;
  12.     #addNode() will add a node to the list  
  13.     def addNode(self, data):
  14.         #Create a new node  
  15.         newNode = Node(data);
  16.         #If list is empty  
  17.         if(self.head == None):
  18.             #Both head and tail will point to newNode  
  19.             self.head = self.tail = newNode;
  20.             #head’s previous will point to None  
  21.             self.head.previous = None;
  22.             #tail’s next will point to None, as it is the last node of the list  
  23.             self.tail.next = None;
  24.         else:
  25.             #newNode will be added after tail such that tail’s next will point to newNode  
  26.             self.tail.next = newNode;
  27.             #newNode’s previous will point to tail  
  28.             newNode.previous = self.tail;
  29.             #newNode will become new tail  
  30.             self.tail = newNode;
  31.             #As it is last node, tail’s next will point to None  
  32.             self.tail.next = None;
  33.     #searchNode() will search a given node in the list  
  34.     def searchNode(self, value):
  35.         i = 1;
  36.         flag = False;
  37.         #Node current will point to head  
  38.         current = self.head;
  39.         #Checks whether the list is empty  
  40.         if(self.head == None):
  41.             print(“List is empty”);
  42.             return;
  43.         while(current != None):
  44.             #Compare value to be searched with each node in the list  
  45.             if(current.data == value):
  46.                 flag = True;
  47.                 break;
  48.             current = current.next;
  49.             i = i + 1;
  50.         if(flag):
  51.             print(“Node is present in the list at the position : “ + str(i));
  52.         else:
  53.             print(“Node is not present in the list”);
  54. dList = SearchList();
  55. #Add nodes to the list  
  56. dList.addNode(1);
  57. dList.addNode(5);
  58. dList.addNode(4);
  59. dList.addNode(2);
  60. dList.addNode(3);
  61. #Search for node 4 in the list  
  62. dList.searchNode(4);
  63. #Search for node 9 in the list  
  64. dList.searchNode(9);

Output:

Node is present in the list at the position: 3
Node is not present in the list

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