diff --git a/Sprint-2/implement_linked_list/linked_list.py b/Sprint-2/implement_linked_list/linked_list.py index e69de29..77d031a 100644 --- a/Sprint-2/implement_linked_list/linked_list.py +++ b/Sprint-2/implement_linked_list/linked_list.py @@ -0,0 +1,59 @@ +# `push_head` should add an element to the start of the list. It should return something that can be passed to +# `remove` to remove that element in the future. +# `pop_tail` should remove an element from the end of the list. +# `remove` takes a handle from `push_head`, and removes that element from the list. + +class Node: + def __init__(self, value): + self.value = value + self.prev = None + self.next = None + + +class LinkedList: + def __init__(self): + self.head = None + self.tail = None + + # adding a new value in the front of the list + def push_head(self, value): + node = Node(value) + + if self.head is None: # if list is empty head and tail becomes this node. + self.head = node + self.tail = node + else: + node.next = self.head + self.head.prev = node + self.head = node + + return node # returns the node so we can remove it later + + # removing last element + def pop_tail(self): + if self.tail is None: + raise Exception("List is empty") + + value = self.tail.value # value to return + + if self.head == self.tail: # if only one element + self.head = None + self.tail = None + else: + self.tail = self.tail.prev # move tail back + self.tail.next = None # remove old tail connection + + return value + + # removes a specific node + def remove(self, node): + + if node.prev is None: # if removing head + self.head = node.next + else: + node.prev.next = node.next # connect previous to next + + if node.next is None: # if removing tail + self.tail = node.prev + else: + node.next.prev = node.prev # connect next to previous \ No newline at end of file