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>
typedef struct list{
	int key;
	struct list *next ;
}list;

list* insert(list* h,int k){
	list* x;
	x = (list*)malloc(sizeof(list));
	x->next = h;
	x->key = k;
//	printf("insert\n");
	return x;
}

list* delete(list* h,int k){
	list* x;
//	list* t;
	list* ins;
	x = h;
//	printf("delete\n");
	if(h->key==k){
		h = h->next;
		ins = x;
		free(ins);
		return h;
	}
	while(x->next!=NULL){
		if((x->next)->key==k){
			ins = x->next;
			x->next = ins->next;
			free(ins);
			return h;
		}else{
			x = x->next;
		}
	}
	return h;
}

list* deleteFirst(list* h){
	list* ins;
	ins = h;
	h = h->next;
	free(ins);
	return h;
}

list* deleteLast(list* h){
	list* x;
	list* ins;
	x = h;
	if(h->next==NULL){
		free(h);
		return NULL;
	}

	while((x->next)->next!=NULL){
		x = x->next;
	}

	ins = x->next;	
	free(ins);
	x->next = NULL;
	return h;
}

int main(int argc, char argv[]){
	int n;
	char command[20] = "\0";
	int d;
	list* head;
	list* x;
	head = NULL;

	scanf("%d",&n);

	int i,j;
	for(i=0;i<n;i++){
		scanf("%s %d",command,&d);
		if(!strcmp(command,"insert"))head = insert(head,d);
		else if(!strcmp(command,"delete"))head = delete(head,d);
		else if(!strcmp(command,"deleteFirst"))head = deleteFirst(head);
		else if(!strcmp(command,"deleteLast"))head = deleteLast(head);
		else printf("The command does not exist.\n");
//		printf("%s %d\n",command,d);

/*		j=0;
	x = head;
	if(x!=NULL)printf("%d",x->key);
	x = x->next;
	while(x != NULL&&j<22){
		printf(" ");
		printf("%d",x->key);
		x = x->next;
		j++;
	}
	printf("\n");
*/	}

	x = head;
	if(x!=NULL)printf("%d",x->key);
	x = x->next;
	while(x != NULL){
		printf(" ");
		printf("%d",x->key);
		x = x->next;
	}
	printf("\n");

	return 0;
}