Python Data Structures - Doubly Linked List Other Related Topics

Python - Search an element in the Doubly Linked List



Searching an element in a doubly linked list requires creating a temp node pointing to the head of the list. Along with this, two more variables are required to track search and track index of the current node. If the temp node is not null at the start, then traverse the list to check if current node value matches with the search value. If it matches then update search tracker variable and stop traversing the list, else keep on traversing the list. If the temp node is empty at the start, then the list contains no item.

The function SearchElement is created for this purpose. It is a 4-step process.

def SearchElement(self, searchValue):
  
  #1. create a temp node pointing to head
  temp = self.head
  
  #2. create two variables: found - to track
  #   search, idx - to track current index
  found = 0
  i = 0 

  #3. if the temp node is not null check the
  #   node value with searchValue, if found 
  #   update variables and break the loop, else
  #   continue searching till temp node is not null 
  if(temp != None):
    while (temp != None):
      i += 1
      if(temp.data == searchValue):
        found += 1
        break
      temp = temp.next
    if(found == 1):
      print(searchValue,"is found at index =", i)
    else:
      print(searchValue,"is not found in the list.")
  else:
    
    #4. If the temp node is null at the start, 
    #   the list is empty
    print("The list is empty.")

The below is a complete program that uses above discussed concept to search an element in a given doubly linked list.

# node structure
class Node:
  def __init__(self, data):
    self.data = data
    self.next = None
    self.prev = None

#class Linked List
class LinkedList:
  def __init__(self):
    self.head = None

  #Add new element at the end of the list
  def push_back(self, newElement):
    newNode = Node(newElement)
    if(self.head == None):
      self.head = newNode
      return
    else:
      temp = self.head
      while(temp.next != None):
        temp = temp.next
      temp.next = newNode
      newNode.prev = temp

  #Search an element
  def SearchElement(self, searchValue):
    temp = self.head
    found = 0
    i = 0 

    if(temp != None):
      while (temp != None):
        i += 1
        if(temp.data == searchValue):
          found += 1
          break
        temp = temp.next
      if(found == 1):
        print(searchValue,"is found at index =", i)
      else:
        print(searchValue,"is not found in the list.")
    else:
      print("The list is empty.")

  #display the content of the list
  def PrintList(self):
    temp = self.head
    if(temp != None):
      print("The list contains:", end=" ")
      while (temp != None):
        print(temp.data, end=" ")
        temp = temp.next
      print()
    else:
      print("The list is empty.")

# test the code                  
MyList = LinkedList()

#Add three elements at the end of the list.
MyList.push_back(10)
MyList.push_back(20)
MyList.push_back(30)

#traverse to display the content of the list.
MyList.PrintList()

#search for element in the list
MyList.SearchElement(10)
MyList.SearchElement(15)
MyList.SearchElement(20)

The above code will give the following output:

The list contains: 10 20 30 
10 is found at index = 1.
15 is not found in the list.
20 is found at index = 2.

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