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 *prev,*next;
};

void init();
void insert(int );
struct Node* listSearch(int );
void delete_N(struct Node *);
void delete_K(int );
void deleteFirst();
void deleteLast();

struct Node *nil;

int main(){
  int n=0;
  int key=0;
  int i=0;
  char order[20];
  char space[2];
  struct Node *now;

  scanf("%d%c",&n,&space[0]);
  init();
  for(i=0;i<n;i++){
    scanf("%s%d%c",order,&key,&space[0]);
    if(order[0]=='i'){
      insert(key);
    }
    else if(order[0]=='d')
      {
	if(order[6]=='F')deleteFirst();
	else if(order[6]=='L')deleteLast();
	else {
	  delete_K(key);
	}
      }
  }
  now=nil->next;
  i=0;
  while(1){
    if(now==nil)break;
    if(i!=0) printf(" ");
    printf("%d",now->key);
    now=now->next;
    i++;
  }
  printf("\n");
  return 0;
}

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

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

struct Node* listSearch(int k){
  struct Node *now;
  now=nil->next;
  while(now != nil && now->key !=k) now=now->next;

  return now;
}

void delete_N(struct Node *t){
  if(t!=nil){
    t->prev->next=t->next;
    t->next->prev=t->prev;
    free(t);
  } 
}

void delete_K(int k){
  delete_N(listSearch(k));
}

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

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