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<string.h>
#include<stdlib.h>

typedef struct Node {
  int key;
  struct Node *prev,*next;
} node;

node *nil;


node* listSearch(int key);
void init(void);
void Print(void);
void deleteNode(node *t);
void deleteFirst(void);
void deleteLast(void);
void deleteKey(int key);
void Insert(int key);

  

int main(void){
  int key;
  int i,n;
  char order[100];
  int np = 0,nd = 0;
  int size = 0;
    
  scanf("%d",&n);
    
  init();
    
  for(i = 0;i < n;i++){
    scanf("%s %d",order,&key);
    
    if(order[0] == 'i'){
      Insert(key);
      np++;
      size++;
      
    } else if(order[0] == 'd'){
      if(strlen(order) > 6){
	
	if(order[6] == 'F'){
	  deleteFirst();
	} else if(order[6] == 'L'){
	  deleteLast();
	}
	
      } else {
	deleteKey(key);
	nd++;
      }
      size--;
    }
  }
    
  Print();
    
  return 0;
}






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



void init(void){ //リストの初期化
  nil = (node *)malloc(sizeof(node));
  
  nil->next = nil;
  nil->prev = nil;
}



void Print(void){
  node *cur = nil->next;
  int i = 0;
  
  while(1){
    if( cur == nil) break;
    if( i++>0 ) printf(" ");
    printf("%d",cur->key);
    cur = cur->next;
  }
  
  puts("");
}



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



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



void deleteKey(int key){
  deleteNode(listSearch(key));
}



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;
}



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