diff --git a/data_structures/linked_list/__init__.py b/data_structures/linked_list/__init__.py index 6d50f23c1f1a..3ddfea5c5abf 100644 --- a/data_structures/linked_list/__init__.py +++ b/data_structures/linked_list/__init__.py @@ -3,12 +3,15 @@ def __init__(self, item, next): self.item = item self.next = next + class LinkedList: def __init__(self): self.head = None + self.size = 0 def add(self, item): self.head = Node(item, self.head) + self.size += 1 def remove(self): if self.is_empty(): @@ -16,7 +19,28 @@ def remove(self): else: item = self.head.item self.head = self.head.next + self.size -= 1 return item def is_empty(self): return self.head is None + + def __len__(self): + """ + >>> linked_list = LinkedList() + >>> len(linked_list) + 0 + >>> linked_list.add("a") + >>> len(linked_list) + 1 + >>> linked_list.add("b") + >>> len(linked_list) + 2 + >>> _ = linked_list.remove() + >>> len(linked_list) + 1 + >>> _ = linked_list.remove() + >>> len(linked_list) + 0 + """ + return self.size diff --git a/data_structures/linked_list/doubly_linked_list.py b/data_structures/linked_list/doubly_linked_list.py index 75b1f889dfc2..e449ed6ec8ac 100644 --- a/data_structures/linked_list/doubly_linked_list.py +++ b/data_structures/linked_list/doubly_linked_list.py @@ -1,77 +1,84 @@ -''' -- A linked list is similar to an array, it holds values. However, links in a linked list do not have indexes. +""" +- A linked list is similar to an array, it holds values. However, links in a linked + list do not have indexes. - This is an example of a double ended, doubly linked list. - Each link references the next link and the previous one. -- A Doubly Linked List (DLL) contains an extra pointer, typically called previous pointer, together with next pointer and data which are there in singly linked list. - - Advantages over SLL - IT can be traversed in both forward and backward direction.,Delete operation is more efficent''' -from __future__ import print_function +- A Doubly Linked List (DLL) contains an extra pointer, typically called previous + pointer, together with next pointer and data which are there in singly linked list. + - Advantages over SLL - IT can be traversed in both forward and backward direction., + Delete operation is more efficient""" -class LinkedList: #making main class named linked list +class LinkedList: # making main class named linked list def __init__(self): self.head = None self.tail = None - + def insertHead(self, x): - newLink = Link(x) #Create a new link with a value attached to it - if(self.isEmpty() == True): #Set the first element added to be the tail + newLink = Link(x) # Create a new link with a value attached to it + if self.isEmpty(): # Set the first element added to be the tail self.tail = newLink else: - self.head.previous = newLink # newLink <-- currenthead(head) - newLink.next = self.head # newLink <--> currenthead(head) - self.head = newLink # newLink(head) <--> oldhead - + self.head.previous = newLink # newLink <-- currenthead(head) + newLink.next = self.head # newLink <--> currenthead(head) + self.head = newLink # newLink(head) <--> oldhead + def deleteHead(self): temp = self.head - self.head = self.head.next # oldHead <--> 2ndElement(head) - self.head.previous = None # oldHead --> 2ndElement(head) nothing pointing at it so the old head will be removed - if(self.head is None): - self.tail = None #if empty linked list + self.head = self.head.next # oldHead <--> 2ndElement(head) + # oldHead --> 2ndElement(head) nothing pointing at it so the old head will be + # removed + self.head.previous = None + if self.head is None: + self.tail = None # if empty linked list return temp - + def insertTail(self, x): newLink = Link(x) - newLink.next = None # currentTail(tail) newLink --> - self.tail.next = newLink # currentTail(tail) --> newLink --> - newLink.previous = self.tail #currentTail(tail) <--> newLink --> - self.tail = newLink # oldTail <--> newLink(tail) --> - + newLink.next = None # currentTail(tail) newLink --> + self.tail.next = newLink # currentTail(tail) --> newLink --> + newLink.previous = self.tail # currentTail(tail) <--> newLink --> + self.tail = newLink # oldTail <--> newLink(tail) --> + def deleteTail(self): temp = self.tail - self.tail = self.tail.previous # 2ndLast(tail) <--> oldTail --> None - self.tail.next = None # 2ndlast(tail) --> None + self.tail = self.tail.previous # 2ndLast(tail) <--> oldTail --> None + self.tail.next = None # 2ndlast(tail) --> None return temp - + def delete(self, x): current = self.head - - while(current.value != x): # Find the position to delete + + while current.value != x: # Find the position to delete current = current.next - - if(current == self.head): + + if current == self.head: self.deleteHead() - - elif(current == self.tail): + + elif current == self.tail: self.deleteTail() - - else: #Before: 1 <--> 2(current) <--> 3 - current.previous.next = current.next # 1 --> 3 - current.next.previous = current.previous # 1 <--> 3 - - def isEmpty(self): #Will return True if the list is empty - return(self.head is None) - - def display(self): #Prints contents of the list + + else: # Before: 1 <--> 2(current) <--> 3 + current.previous.next = current.next # 1 --> 3 + current.next.previous = current.previous # 1 <--> 3 + + def isEmpty(self): # Will return True if the list is empty + return self.head is None + + def display(self): # Prints contents of the list current = self.head - while(current != None): + while current is not None: current.displayLink() - current = current.next + current = current.next print() + class Link: - next = None #This points to the link in front of the new link - previous = None #This points to the link behind the new link + next = None # This points to the link in front of the new link + previous = None # This points to the link behind the new link + def __init__(self, x): self.value = x + def displayLink(self): - print("{}".format(self.value), end=" ") + print(f"{self.value}", end=" ")