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>
#include <string.h>

struct node {
	int value;
	struct node *next;
	struct node *prev;
};

typedef struct node NODE;

NODE *nil;
void init();
void insert(int x);
void delete(int x);
void deleteFirst();
void deleteLast();

void init() {
	nil = (NODE *)malloc(sizeof(NODE));
	nil->value = -1;
	nil->next = nil;
	nil->prev = nil;
}

void insert(int x) {
	NODE *tmp, *new, *next, *prev;

	new = (NODE *)malloc(sizeof(NODE));
	new->value = x;
	
	next = nil->next;
//	prev = next->prev;
	new->prev = nil;
	new->next = next;
	next->prev = new;
	nil->next = new;
	return;
}

void delete(int x) {
	NODE *inode, *next, *prev;
	for (inode = nil->next; inode->value != -1; inode = inode->next) {
		if (inode->value == x) {
			next = inode->next;
			prev = inode->prev;
			free(inode);
			prev->next = next;
			next->prev = prev;
			break;
		}
	}
	return;
}

void deleteFirst() {
	NODE *delete, *next, *prev;
	delete = nil->next;
	if (delete->value == -1) return;
	next = delete->next;
	prev = delete->prev;
	free(delete);
	prev->next = next;
	next->prev = prev;
	return;
}

void deleteLast() {
	NODE *delete, *next, *prev;
	delete = nil->prev;
	if (delete->value == -1) return;
	next = delete->next;
	prev = delete->prev;
	free(delete);
	prev->next = next;
	next->prev = prev;
	return;	
}

void showList() {
	NODE *inode;
//	printf("nil->value = %d\n", nil->value);
	for (inode = nil->next; inode->value != -1; inode = inode->next) {
		if (inode->next->value != -1) {
			printf("%d ", inode->value);
		} else {
			printf("%d\n", inode->value);
		}
	}
//	printf("\n");
}

int main(void) {
	int n, i, value;
	char cmd[20] = {0};
	
	init();
	scanf("%d", &n);

	for (i = 0; i < n; ++i) {
		scanf("%s", cmd);
		if (strcmp(cmd, "insert") == 0) {
			scanf(" %d", &value);
//			printf("%s %d\n", cmd, value);
			insert(value);
		} else if (strcmp(cmd, "delete") == 0) {
			scanf(" %d", &value);
//			printf("%s %d\n", cmd, value);
			delete(value);
		} else if (strcmp(cmd, "deleteFirst") == 0) {
//			printf("%s\n", cmd);
			deleteFirst();
		} else {
//			printf("%s\n", cmd);
			deleteLast();
		}
//		showList();
	}

	showList();
	
	
	return 0;
}