Linked_List_Construction.py

# https://www.algoexpert.io/questions/Linked%20List%20Construction
# Write a class for a Doubly Linked List.


# Definition for doubly-linked list node.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#         self.prev = prev

class DoublyLinkedList:

    def __init__(self):
        self.head = None
        self.tail = None

    # O(1) time | O(1) space
    def set_head(self, node):
        if self.head is None:
            self.head = node
            self.tail = node
            return
        self.insert_before(self.head, node)

    # O(1) time | O(1) space
    def set_tail(self, node):
        if self.tail is None:
            self.set_head(node)
            return
        self.insert_after(self.tail, node)

    # O(1) time | O(1) space
    def insert_before(self, node, node_to_insert):
        if node_to_insert == self.head and node_to_insert == self.tail:
            return
        self.remove(node_to_insert)
        node_to_insert.prev = node.prev
        node_to_insert.next = node
        if node.prev is None:
            self.head = node_to_insert
        else:
            node.prev.next = node_to_insert
        node.prev = node_to_insert

    # O(1) time | O(1) space
    def insert_after(self, node, node_to_insert):
        if node_to_insert == self.head and node_to_insert == self.tail:
            return
        self.remove(node_to_insert)
        node_to_insert.prev = node
        node_to_insert.next = node.next
        if node.next is None:
            self.tail = node_to_insert
        else:
            node.next.prev = node_to_insert
        node.next = node_to_insert

    # O(p) time | O(1) space
    def insert_at_position(self, position, node_to_insert):
        if position == 1:
            self.set_head(node_to_insert)
            return
        node = self.head
        current_position = 1
        while node is not None and current_position != position:
            node = node.next
            current_position += 1
        if node is not None:
            self.insert_before(node, node_to_insert)
        else:
            self.set_tail(node)

    # O(n) time | O(1) space
    def remove_nodes_with_value(self, value):
        node = self.head
        while node is not None:
            node_to_remove = node
            node = node.next
            if node_to_remove.value == value:
                self.remove(node_to_remove)

    # O(1) time | O(1) space
    def remove(self, node):
        if node == self.head:
            self.head = self.head.next
        if node == self.tail:
            self.tail = self.tail.prev
        self.remove_node_bindings(node)

    def contains_node_with_value(self,  value):
        node = self.head
        while node is not None and node.value != value:
            node = node.next
        return node is not None

    def remove_node_bindings(self, node):
        if node.prev is not None:
            node.prev.next = node.next
        if node.next is not None:
            node.next.prev = node.prev
        node.next = None
        node.prev = None