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.
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
Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.
The number of operations ≤ 2,000,000
The number of delete operations ≤ 20
0 ≤ value of a key ≤ 10^9
The number of elements in the list does not exceed 10^6
For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.