Problem:
Doubly Linked List

Your task is to implement a double linked list.

Write a program which performs the following operations:

insert x: insert an element with key x into the front of the list.

delete x: delete the first element which has the key of x from the list. If there is not such element, you need not do anything.

deleteFirst: delete the first element from the list.

deleteLast: delete the last element from the list.

Input

The input is given in the following format:

n

command1

command2

...

commandn

In the first line, the number of operations n is given. In the following n lines, the above mentioned operations are given in the following format:

insert x

delete x

deleteFirst

deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

The number of operations ≤ 2,000,000

The number of delete operations ≤ 20

0 ≤ value of a key ≤ 109

The number of elements in the list does not exceed 106

For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

Solution in Python (judge verdict: Runtime Error)

#!/usr/bin/python
# -*- coding:utf-8 -*-

class Node(object):
    def __init__(self, data, prev_node, next_node):
        self.data = data
        self.prev_node = prev_node
        self.next_node = next_node

class DoubleList(object):
    head = None
    tail = None

    def insert(self, data):
        new_node = Node(data, None, None)
        if self.head is None:
            self.head = self.tail = new_node
        else:
            new_node.next_node = self.head
            new_node.prev_node = None
            self.head.prev_node = new_node
            self.head = new_node

    def delete(self, data_value):
        current_node = self.head
        while current_node is not None:
            if current_node.data == data_value:
                if current_node.prev_node is not None and current_node.next_node is not None:
                    current_node.prev_node.next_node = current_node.next_node
                    current_node.next_node.prev_node = current_node.prev_node
                elif current_node.prev_node is None:
                    self.head = current_node.next_node
                    current_node.next_node.prev_node = None
                elif current_node.next_node is None:
                    self.tail = current_node.prev_node
                    current_node.prev_node.next_node = None
            current_node = current_node.next_node

    def deleteFirst(self):
        if self.head.next_node is not None:
            self.head.next_node.prev_node = None
            self.head = self.head.next_node
        else:
            self.head = self.tail = None

    def deleteLast(self):
        if self.tail.prev_node is not None:
            self.tail.prev_node.next_node = None
            self.tail = self.tail.prev_node
        else:
            self.head = self.tail = None

    def show(self):
        current_node = self.head
        data = ""
        while current_node is not None:
            data += current_node.data+" "
            current_node = current_node.next_node
        print data[:-1]

if __name__ == "__main__":
    DL = DoubleList()
    num = int(raw_input())
    for i in range(num):
        line = raw_input()
        if " " in line:
            operation = line.strip().split()[0]
            value = line.strip().split()[1]
        else:
            operation = line.strip()

        if operation == "insert":
            DL.insert(value)
        elif operation == "delete":
            DL.delete(value)
        elif operation == "deleteFirst":
            DL.deleteFirst()
        else:
            DL.deleteLast()

    DL.show()