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.util.Scanner;
public class Main{
    public static void main(String[] args){
        Scanner s=new Scanner(System.in);
        int n=s.nextInt(),first=0,num=1,last=0;
        int list[]=new int[2000000];
        int before[]=new int[2000000];
        int next[]=new int[2000000];

        for(int i=0;i<n;i++){
            String o=s.next();
            if(o.equals("insert")){
                list[num]=s.nextInt();
                if(first==0) last=num;
                before[first]=num;
                next[num]=first;
                first=num;
                num++;
            }else if(o.equals("delete")){
                int d=s.nextInt();
                int j=first;
                while(j!=0){
                    if(d==list[j]){
                        if(j==last&&j==first){
                            first=0;
                            last=0;
                        }else if(j==last){
                            last=before[last];
                            next[last]=0;
                        }else if(j==first){
                            first=next[j];
                            before[first]=0;
                        }else{
                            next[before[j]]=next[j];
                            before[next[j]]=before[j];
                        }
                        break;
                    }
                    j=next[j];
                }
            }else if(o.equals("deleteFirst")){
                if(first==last){
                    first=0;
                    last=0;
                }else{
                    first=next[first];
                    before[first]=0;
                }
            }else{
                if(first==last){
                    first=0;
                    last=0;
                }else{
                    last=before[last];
                    next[last]=0;
                }
            }
        }
        int soeji=first;
        while(soeji!=0){
            System.out.print(list[soeji]);
            soeji=next[soeji];
            if(soeji!=0) System.out.print(" ");
        }
        System.out.println("");
    }
}