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: Accepted)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Cell {
	int data;
	Cell next;
	Cell prev;

	Cell(int data) {
		this.data = data;
	}
}

class DLList {
	final Cell header;

	DLList() {
		header = new Cell(-1);
		header.next = header;
		header.prev = header;
	}
	void insert(int x) {
		Cell c = new Cell(x);
		Cell d = header.next;
		c.next = d;
		c.prev = header;
		header.next = c;
		d.prev = c;
	}
	Cell search(int x) {
		Cell c = header.next;
		while(c.data != x) {
			c = c.next;
			if(c == header) {
				return header;
			}
		}
		return c;
	}
	void delete(int x) {
		Cell c = search(x);
		if(c == header) {

		} else {
			c.prev.next = c.next;
			c.next.prev = c.prev;
		}
		c = null;
	}
	void deleteFirst() {
		Cell c = header.next;
		header.next = c.next;
		c.next.prev = header;
		c = null;
	}
	void deleteLast() {
		Cell c = header.prev;
		c.prev.next = header;
		header.prev = c.prev;
		c = null;
	}
}

//双方向連結リスト
public class Main {
	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		DLList list = new DLList();
		try {
			int n = Integer.parseInt(br.readLine());
			for(int i = 0; i < n; i++) {
				String[] str = br.readLine().split(" ");
				if(str[0].startsWith("i")) {
					int a = Integer.parseInt(str[1]);
					list.insert(a);
				} else if(str[0].equals("deleteFirst")) {
					list.deleteFirst();
				} else if(str[0].equals("deleteLast")) {
					list.deleteLast();
				} else {
					int a = Integer.parseInt(str[1]);
					list.delete(a);
				}
			}
			Cell c = list.header.next;
			while(c != list.header) {
				if(c.next == list.header) {
					System.out.println(c.data);
				} else {
					System.out.print(c.data + " ");
				}
				c = c.next;
			}
		} catch(IOException e) {
			System.out.println("error");
		} finally {
			try {
				br.close();
			} catch(IOException e) {

			}
		}
	}

}