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"
	"strings"
)

type dlist struct {
	value int
	prev  *dlist
	next  *dlist
}

var head, last *dlist

var sc = bufio.NewScanner(os.Stdin)

func nextLine() string {
	sc.Scan()
	return sc.Text()
}

func main() {
	var (
		n int
	)
	head = new(dlist)
	last = new(dlist)
	head.next = last
	last.prev = head

	fmt.Scan(&n)
	for i := 0; i < n; i++ {
		s := nextLine()
		switch s {
		case "deleteFirst":
			deleteFirst()
		case "deleteLast":
			deleteLast()
		default:
			ss := strings.Split(s, " ")
			switch ss[0] {
			case "insert":
				value, _ := strconv.Atoi(ss[1])
				insert(value)
			case "delete":
				value, _ := strconv.Atoi(ss[1])
				deleteC(value)
			}
		}
	}

	dl := head.next
	fmt.Print(dl.value)
	dl = dl.next
	for {
		if dl == last {
			break
		}
		fmt.Print(" ", dl.value)
		dl = dl.next
	}
	fmt.Println()
}

func insert(v int) {
	dl := new(dlist)
	dl.value = v
	dl.prev = head
	dl.next = head.next

	head.next = dl
	dl.next.prev = dl
}

func deleteC(v int) {
	dl := head.next
	for dl != last {
		if dl.value == v {
			dl.prev.next = dl.next
			dl.next.prev = dl.prev
			return
		}
		dl = dl.next
	}
}

func deleteFirst() {
	head.next = head.next.next
	head.next.prev = head
}

func deleteLast() {
	last.prev.prev.next = last
	last.prev = last.prev.prev
}