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++ (judge verdict: Time Limit Exceeded)

#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

const int inf = 1000000;

int lleft[inf], lright[inf];
int first = inf, last = inf;

void link(int l, int r){
    lright[l] = r;
    lleft[r] = l;
}

void init(){
    for(int i = 0; i < inf; i++){
        lleft[i] = lright[i] = inf;
    }
    lleft[first] = last;
    lright[last] = first;
}

int main(){
    char cmd[25];
    int key;

    init();
    int kase;
    scanf("%d",&kase);

    while(kase--){
        scanf("%s",cmd);
//        scanf("%d",&key);

        if(cmd[0] == 'i'){
            scanf("%d",&key);
            link(key,first);
            first = key;
            last = lleft[first];

//            int i;
//            for(i = first; lright[i] != inf; i = lright[i]) {}
//            last = i;
        }else if(cmd[0] == 'd'){
            if(strlen(cmd) > 6){
                if(cmd[6] == 'F'){
                    //delete first
                    link(lleft[first],lright[first]);
                    first = lright[first];
                } else if (cmd[6] == 'L'){
                    //delete last
                    link(lleft[last],lright[last]);
                    last = lleft[last];
                }
            }
            if(strlen(cmd) <= 6){
                scanf("%d",&key);
                link(lleft[key],lright[key]);
            }
        }
    }
//    cout << first << endl;
//    int i;
//    for(i = first; lright[i] != inf; i = lright[i]){
//        printf("%d ",i);
//    }
//    last = i;
//    printf("%d\n",i);

    int i;
    for(i = first; lright[i] != last; i = lright[i]){
        printf("%d ",i);
    }
    printf("%d\n",i);

}