Max Stack — LeetCode 716 Python Solution

class Node:
    def __init__(self, val=0):
        self.val = val
        self.prev: Union[Node, None] = None
        self.next: Union[Node, None] = None


class DoubleLinkedList:
    def __init__(self):
        self.head = Node()
        self.tail = Node()
        self.head.next = self.tail
        self.tail.prev = self.head

    def append(self, val) -> Node:
        node = Node(val)
        node.next = self.tail
        node.prev = self.tail.prev
        self.tail.prev = node
        node.prev.next = node
        return node

    @staticmethod
    def remove(node) -> Node:
        node.prev.next = node.next
        node.next.prev = node.prev
        return node

    def pop(self) -> Node:
        return self.remove(self.tail.prev)

    def peek(self):
        return self.tail.prev.val


class MaxStack:
    def __init__(self):
        self.stk = DoubleLinkedList()
        self.sl = SortedList(key=lambda x: x.val)

    def push(self, x: int) -> None:
        node = self.stk.append(x)
        self.sl.add(node)

    def pop(self) -> int:
        node = self.stk.pop()
        self.sl.remove(node)
        return node.val

    def top(self) -> int:
        return self.stk.peek()

    def peekMax(self) -> int:
        return self.sl[-1].val

    def popMax(self) -> int:
        node = self.sl.pop()
        DoubleLinkedList.remove(node)
        return node.val


# Your MaxStack object will be instantiated and called as such:
# obj = MaxStack()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.peekMax()
# param_5 = obj.popMax()