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 Go (judge verdict: Time Limit Exceeded)

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

type Node struct {
	Value int
	Next  *Node
	Prev  *Node
}

type DoublyLinkedList struct {
	Head *Node
	Tail *Node
}

func (l *DoublyLinkedList) insert(x int) {
	n := l.Head
	l.Head = &Node{
		Value: x,
		Next:  n,
		Prev:  nil,
	}
	if n != nil {
		n.Prev = l.Head
	}
	if l.Tail == nil {
		l.Tail = l.Head
	}
}

func (l *DoublyLinkedList) delete(x int) {
	n1 := l.Head
	n2 := l.Head.Next
	for x != n1.Value && x != n2.Value {
		if n1.Next != nil && n1.Next.Next != nil {
			n1 = n1.Next.Next
		}
		if n2.Next != nil && n2.Next.Next != nil {
			n2 = n2.Next.Next
		}
	}
	var n *Node
	if x == n1.Value {
		n = n1
	} else if x == n2.Value {
		n = n2
	}
	if n != nil {
		// 削除
		if n.Prev != nil {
			n.Prev.Next = n.Next
		}
		if n.Next != nil {
			n.Next.Prev = n.Prev
		}
		// 先頭要素が削除された場合
		if n.Prev == nil {
			l.Head = n.Next
		}
		// 最後尾要素が削除された場合
		if n.Next == nil {
			l.Tail = n.Prev
		}
	}
}

func (l *DoublyLinkedList) deleteFirst() {
	n := l.Head
	if n.Next != nil {
		n.Next.Prev = nil
		l.Head = n.Next
	} else {
		l.Head = nil
		l.Tail = nil
	}
}

func (l *DoublyLinkedList) deleteLast() {
	n := l.Tail
	if n.Prev != nil {
		n.Prev.Next = nil
		l.Tail = n.Prev
	} else {
		l.Head = nil
		l.Tail = nil
	}
}

func (l *DoublyLinkedList) println() {
	n := l.Head
	fmt.Print(n.Value)
	for n.Next != nil {
		n = n.Next
		fmt.Print(" ")
		fmt.Print(n.Value)
	}
	fmt.Println("")
}

func nextStr(sc *bufio.Scanner) string {
	sc.Scan()
	s := sc.Text()
	return s
}

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	n, err := strconv.Atoi(sc.Text())
	if err != nil {
		panic(err)
	}
	return n
}

func main() {
	sc := bufio.NewScanner(os.Stdin)
	sc.Split(bufio.ScanWords)

	var l DoublyLinkedList
	n := nextInt(sc)
	for i := 0; i < n; i++ {
		s := nextStr(sc)
		switch s {
		case "insert":
			x := nextInt(sc)
			l.insert(x)
		case "delete":
			x := nextInt(sc)
			l.delete(x)
		case "deleteFirst":
			l.deleteFirst()
		case "deleteLast":
			l.deleteLast()
		}
	}
	l.println()
}