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 C++14 (judge verdict: Time Limit Exceeded)

#include <iostream>
#include <string>

struct List{
    int value[1000000]={-1};
    int next[1000000]={-1};
    int prev[1000000]={-1};
    int head = -1;
    int tail = -1;
    int idx = 0;
    
    void insertion(int x){
        next[idx] = head;
        prev[head] = idx;
        if(tail==-1){
            tail = idx;
        }
        value[idx] = x;
        head = idx;
        idx++;
    }

    int serch(int x){
        int j = head;
        while(j!=-1){
            if(value[j]==x){
                return j;
            }
            j = next[j];
        }
        return -1;
    }

    void deleteFirst(){
        int nh = next[head];
        if(nh==-1){
            head = -1;
            tail = -1;
        }else{
            head = nh;
            prev[head] = -1;
        }
    }

    void deleteLast(){
        int pt = prev[tail];
        if(pt==-1){
            head = -1;
            tail = -1;
        }else{
            tail = pt;
            next[tail] = -1;
        }
    }

    void del(int x){
        int s = serch(x);
        if(s!=-1){
            if(s==head){
                deleteFirst();
            }else if(s==tail){
                deleteLast();
            }else{
                int n = next[s];
                int p = prev[s];
                next[p] = n;
                prev[n] = p;
            }
        }
    }

    void command(std::string str){
        if(str=="insert"){
            int x;
            std::cin >> x;
            insertion(x);
        }
        if(str=="delete"){
            int x;
            std::cin >> x;
            del(x);
        }
        if(str=="deleteFirst"){
            deleteFirst();
        }
        if(str=="deleteLast"){
            deleteLast();
        }
    }

    void print(){
        int k = head;
        while(k!=-1){
            std::cout << value[k];
            k = next[k];
            if(k!=-1){
                std::cout << " ";
            }
        }
        std::cout << "\n";
    }
};


int main(){
    List lst;
    int n;
    std::cin >> n;
    for(int i=0;i<n;i++){
        std::string str;
        std::cin >> str;
        lst.command(str);
    }
    lst.print();
    return 0;
}