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 JAVA (judge verdict: Time Limit Exceeded)


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

class Main{

	public static void main(String[] args) {

		try {
			List<String> list = new ArrayList<String>();
			BufferedReader r =
                new BufferedReader(new InputStreamReader(System.in), 1);
			String strInput = r.readLine();
			String[] strcmd;
			int loopmax = Integer.parseInt(strInput);
			int tempIdx;

			for(int i=0;i<loopmax;i++) {
				strInput = r.readLine();
				strcmd = strInput.split(" ");

				if(strcmd[0].equals("insert")) {
					list.add(0,strcmd[1]);
				}else if(strcmd[0].equals("deleteFirst")) {
					list.remove(0);
				}else if(strcmd[0].equals("deleteLast")) {
					list.remove(list.size()-1);
				}else if(strcmd[0].equals("delete")) {
					tempIdx = list.indexOf(strcmd[1]);
					if(tempIdx>=0){
						list.remove(tempIdx);
					}
				}
			}

			StringBuffer sb = new StringBuffer();
			int listSize = list.size();
			for(int i=0;i<listSize;i++) {
				sb.append(list.get(i)).append(" ");
			}
			String out = sb.toString();
			System.out.println(out.substring(0,out.length()-1));

		} catch (IOException e) {
			e.printStackTrace();
		}

	}
}