doubly_linked.py

class Node:
    def __init__(self, x):
        self.val = x
        self.next = None
        self.prev = None

class DoublyLinkedList:
    def __init__(self):
        self.head = None
        self.tail = None
        self.cnt = 0

    def addHead(self, x):
        node = Node(x)

        if self.cnt == 0:
            self.head = node
            self.tail = self.head

        else:
            node.next = self.head
            self.head.prev = node
            self.head = node

        self.cnt += 1

    def addTail(self, x):
        node = Node(x)

        if self.cnt == 0:
            self.head = node
            self.tail = self.head

        else:
            self.tail.next = node
            node.prev = self.tail
            self.tail = self.tail.next

        self.cnt += 1

    def insert(self, pos, x):
        node = Node(x)
        diff = self.cnt - pos

        if diff < 0 or diff > self.cnt:
            print("Invalid position")
            return

        elif diff == 0:
            self.addTail(x)

        elif diff == self.cnt:
            self.addHead(x)

        else:
            cur = self.head

            while pos > 1:
                cur = cur.next
                pos -= 1

            node.next = cur.next
            node.prev = cur
            cur.next.prev = node
            cur.next = node

        self.cnt += 1

    def removeHead(self):
        if self.cnt == 0:
            return

        elif self.cnt == 1:
            self.head = None
            self.tail = None

        else:
            self.head = self.head.next
            self.head.prev.next = None
            self.head.prev = None

        self.cnt -= 1

    def removeTail(self):
        if self.cnt == 0:
            return

        elif self.cnt == 1:
            self.head = None
            self.tail = None

        else:
            self.tail = self.tail.prev
            self.tail.next.prev = None
            self.tail.next = None

        self.cnt -= 1

    def removePos(self, pos):
        diff = self.cnt - pos

        if diff < 0 or diff > self.cnt:
            print("Invalid position")
            return

        elif diff == 0:
            self.removeTail()

        elif diff == self.cnt:
            self.removeHead()

        else:
            cur = self.head
            while pos > 1:
                cur = cur.next

            cur.next = cur.next.next
            cur.next.prev = cur
            cur = cur.next

        self.cnt -= 1

    def __getitem__(self, item):
        if item < 0 or item > self.cnt - 1:
            print("Invalid position")
            return

        else:
            cur = self.head

            while item > 0:
                cur = cur.next
                item -= 1

            return cur.val

    def size(self):
        return self.cnt

    def empty(self):
        return self.cnt == 0

    def printForward(self):
        cur = self.head

        while cur is not None:
            print(cur.val, end=" ")
            cur = cur.next

        print("")

    def printReverse(self):
        cur = self.tail

        while cur is not None:
            print(cur.val, end = " ")
            cur = cur.prev

        print("")