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>

struct _Node{
  int key;
  struct _Node *next;
  struct _Node *prev;
};
typedef struct _Node Node;

Node *nil;

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

void deleteNode(Node *n) {
  n->prev->next = n->next;
  n->next->prev = n->prev;
}

void delete(int key) {
  Node *n;
  for (n = nil->next; n != nil; n = n->next) {
    if (n->key == key) {
      deleteNode(n);
      return;
    }
  }
}

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

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

int main() {
  nil = (Node *)malloc(sizeof(Node));
  nil->next = nil;
  nil->prev = nil;
  int i, key, N;
  char *command;
  command = (char *)malloc(sizeof(char) * 12);

  scanf("%d", &N);
  for (i = 0; i < N; i++) {
    scanf(" %s", command);
    switch(*command) {
    case 'i': scanf(" %d", &key); insert(key); break;
    default :
      switch(*(command + 6)) {
      case 'F': deleteFirst(); break;
      case 'L': deleteLast(); break;
      default: scanf(" %d", &key); delete(key); break;
      }
    }
  }

  Node *node;
  for (node = nil->next;; node = node->next) {
    if (node->next == nil) {
      printf("%d\n", node->key);
      break;
    }
    printf("%d ", node->key);
  }
  return 0;
}