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;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.LinkedList;

public class Main {
	static String[] dict = new String[1000005];

	public static void main(String[] args) {
		try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
				PrintWriter out = new PrintWriter(System.out);) {

			int n = Integer.parseInt(br.readLine());
			LinkedList<Integer> list = new LinkedList<>();
			br.lines().forEach(str -> {
				String[] tmp = str.split(" ");
				switch (tmp[0]) {
				case "insert":
					// リストの先頭に追加
					list.addFirst(Integer.parseInt(tmp[1]));
					break;

				case "delete":
					// parseIntの戻り値はint型である為、
					// そのまま渡すとremove(int index)が呼び出されてしまう。
					// 明示的にInteger型に変換することで、
					// remove(Object o)メソッドを呼び出す。
					list.remove((Integer) Integer.parseInt(tmp[1]));
					break;

				case "deleteFirst":
					// 先頭の要素を削除
					list.removeFirst();
					break;

				case "deleteLast":
					// 末尾の要素を削除
					list.removeLast();
					break;
				}
			}

			);

			for (Iterator<Integer> it = list.listIterator(); it.hasNext();) {
				out.print(it.next());
				if (it.hasNext()) {
					out.print(" ");
				} else {
					out.println();
				}
			}
			out.flush();

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

	}

	static int getKey(String key) {
		int sum = 0;
		for (int i = 0, p = 0; i < key.length(); i++, p = 5) {
			char cur = key.charAt(i);
			switch (cur) {
			case 'A':
				sum += p * 1;
				break;

			case 'C':
				sum += p * 2;
				break;
			case 'G':
				sum += p * 3;
				break;
			case 'T':
				sum += p * 4;
				break;

			}
		}
		return sum;
	}

	static int h1(String key) {
		return getKey(key) % dict.length;
	}

	static int h2(String key) {
		return 1 + getKey(key) % (dict.length - 1);
	}

	static boolean insert(String key) {
		int h = 0;
		for (int i = 0; h < key.length(); i++) {
			h = (h1(key) + i * h2(key)) % dict.length;
			if (dict[h] == null) {
				dict[h] = key;
				return true;
			} else if (dict[h].equals(key)) {
				continue;
			}
		}
		return false;
	}

	static boolean search(String key) {
		int h = 0;
		for (int i = 0; h < key.length(); i++) {
			h = (h1(key) + i * h2(key)) % dict.length;
			if (dict[h] == null) {
				return false;
			} else if (dict[h].equals(key)) {
				return true;
			}
		}
		return false;
	}

}