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>

struct Linked_List{
  int key;
  struct Linked_List *prev;
  struct Linked_List *next;
};

typedef struct Linked_List Link;

//関数のプロトタイプ宣言
void insert(int);
void delete(int);
void deleteFirst(void);
void deleteLast(void);
void delete_ALL(void);
void Show(void);

Link *nill;

int main(void){
  int n,key;
  int i;
  char input[12];

  scanf("%d",&n);

  //先頭へのポインタをnillに格納
  nill=malloc(sizeof(Link));
  nill->prev=nill;
  nill->next=nill;

  for(i=0;i<n;i++){
    scanf("%s",input);
    
    if(strcmp("insert",input)==0){
      scanf("%d",&key);
      insert(key);
    }
    else if(strcmp("delete",input)==0){
      scanf("%d",&key);
      delete(key);
    }
    else if(strcmp("deleteFirst",input)==0){
      deleteFirst();
    }
    else if(strcmp("deleteLast",input)==0){
      deleteLast();
    }
    else{
      printf("Error\n");
      exit(1);
    }
    
    
  }

  //出力
  Show();

  //解放
  delete_ALL();
  free(nill);

  return 0;
}


//insert関数
void insert(int num){
  Link *data;

  data=malloc(sizeof(Link));
  data->key=num;
  nill->next->prev=data;
  data->next=nill->next;
  nill->next=data;
  data->prev=nill;
}

//delete関数
void delete(int num){
  Link *work;

  work=nill->next;
  while(work->key!=num) work=work->next;
  work->next->prev=work->prev;
  work->prev->next=work->next;
  free(work);
}

//deleteFirst
void deleteFirst(void){
  Link *work;

  work=nill->next;
  work->next->prev=nill;
  nill->next=work->next;
  free(work);
}

//deleteLast
void deleteLast(void){
  Link *work;

  work=nill->next;
  while(work->next!=nill) work=work->next;
  nill->prev=work->prev;
  work->prev->next=nill;
  free(work);
}

//delete_ALL関数
void delete_ALL(void){
  while(nill->next!=nill){
    deleteLast();
  }
}


//Show関数
void Show(void){
  Link *work;

  work=nill->next;
  while(work!=nill){
    if(work==nill->next) printf("%d",work->key);
    else printf(" %d",work->key);
    work=work->next;
  }
  printf("\n");
}