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 <string.h>
#include <stdlib.h>

typedef struct node *link;

struct node{
	int key;
	link next;
	link prev;
};

int main()
{
	int i, n, k;
	char op[20];
	
	link head = malloc(sizeof(*head));
	head->key = -1;
	head->next = NULL;
	head->prev = NULL;
	
	scanf("%d", &n);
	
	for (i = 0; i < n; i++)
	{
		scanf("%s", op);
		
		if(strlen(op) > 6)
		{
			
			if(op[6] == 'F')
			{
				if(head->next != NULL)
				{
					if(head->next->next !=NULL)
					{
						head->next->next->prev = head;
						head->next = head->next->next;
					}else
					{
						head->next = NULL;
					}
				}
			}else if(op[6] == 'L')
			{
				link t = head;
				while(t->next != NULL)
				{
					t = t->next;
				}
				t->prev->next = NULL;
				free(t);
			}
			
		}else
		{
			scanf("%d", &k);
			
			if(op[0] == 'i')
			{
				link t = malloc(sizeof(*t));
				t->key = k;
				t->next = head->next;
				t->prev = head;
				head->next = t;
				if(t->next != NULL)
				{
					t->next->prev = t;
				}
			}else if(op[0] == 'd')
			{
				if(head->next != NULL)
				{
					link t = head->next;
					while(t->next != NULL)
					{
						if(t->key == k)
						{
							t->prev->next = t->next;
							t->next->prev = t->prev;
							free(t);
							break;
						}
						else
						{
							t = t->next;
						}
					}
					if(t->key == k)
					{
						t->prev->next = t->next;
						free(t);
					}
				}
			}
			
		}
	}
	
	if(head->next != NULL)
	{
		link t = head->next;
		while(t->next != NULL)
		{
			printf("%d ", t->key);
			t = t->next;
		}
		printf("%d\n", t->key);
	}
	
	return 0;
}