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: Accepted)

#include <stdio.h>
#include <stdlib.h>
#define LEN 1000005

typedef struct node {
	int key;
	struct node* next;
	struct node* prev;
}NODE;

NODE* nil;

void init() {
	nil = (NODE*)malloc(sizeof(NODE));
	nil->next = nil;
	nil->prev = nil;
}

void insert(int key) {
	NODE* x = (NODE*)malloc(sizeof(NODE));
	x->key = key;
	x->next = nil->next;
	nil->next->prev = x;
	nil->next = x;
	x->prev = nil;
}

NODE* listSearch(int key) {
	NODE* cur = nil->next;
	while (cur != nil && cur->key != key) {
		cur = cur->next;
	}
	return cur;
}

void deleteNode(NODE* t) {
	if (t == nil) return;
	t->next->prev = t->prev;
	t->prev->next = t->next;
	free(t);
}

void deleteFirst() {
	deleteNode(nil->next);
}

void deleteLast() {
	deleteNode(nil->prev);
}

void delteKey(int x) {
	deleteNode(listSearch(x));
}

void printNode() {
	NODE* x = nil->next;
	int isf = 0;
	while (x != nil) {
		if (isf++ > 0) printf(" ");
		printf("%d", x->key);
		x = x->next;
	}
	printf("\n");
}

int main() {
	int i;
	int n;
	int key;
	char com[20];
	scanf("%d", &n);

	init();
	for (i = 0; i < n; i++) {
		scanf("%s%d", com, &key);
		if (strcmp(com, "insert") == 0) {
			insert(key);
		} else if(strcmp(com, "delete") == 0){
			delteKey(key);
		} else if(strcmp(com,"deleteFirst") == 0){
			deleteFirst();
		} else if(strcmp(com, "deleteLast") == 0){
			deleteLast();
		}
	}
	printNode();
	return 0;
}