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 <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 200000

struct node{
    int key;
    struct node *next;
    struct node *prev;
};
typedef struct node * NodePointer;
NodePointer nil;
int num = 0;
void init(){
    nil = malloc(sizeof(struct node));
    nil->next = nil;
    nil->prev = nil;
}

void insert(int key){
    NodePointer x;
    x = malloc(sizeof(struct node));
    x->key = key;
    x->next = nil->next;
    nil->next = x;
    num++;
}

void delete(int key){
    int i=0;
    NodePointer cur = nil;
    if(key == -1){
        nil->next = nil->next->next;
        nil->next->next->prev = nil;
    }
    else if(key == -2){
        while(cur->next->next != nil) cur = cur->next;
        cur->next = nil;
    }
    else{
        while(i < num){
            if(cur->next->key == key) break;
            cur = cur->next;
            i++;
        }
        cur->next = cur->next->next;
        cur->next->next->prev = cur;
    }
    num --;
}

void printList(){
    NodePointer cur = nil->next;
    int isf = 1;
    while(1){
        if ( cur == nil ) break;
        if ( isf == 0)  printf(" ");
        printf("%d", cur->key);
        cur = cur->next;
        isf = 0;
    }
    printf("\n");
}

int main(){
    int i, n, key;
    char s[20];
    init();
    scanf("%d",&n);
    for(i = 0; i < n; i++){
        scanf("%s",s);
        if(s[0] == 'i'){
            scanf("%d",&key);
            insert(key);
        }
        else if(s[0] == 'd'){
            if(s[6] == 'F')
                delete(-1);
            else if(s[6] == 'L')
                delete(-2);
            else{
                scanf("%d",&key);
                delete(key);
            }
        }
    }
    printList();
    return 0;
}