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>


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

Node *nil;

Node* listSearch(int key){
  Node *c = nil->next;
  while(c->key!=key){
    if(c==nil) break;
    c = c->next;
  }
  return c;
}

void printList(){
 struct Node *c = nil->next;
  int isf =1;
  while(1){
    if(c==nil) break;
    if(isf==0) printf(" ");
    printf("%d",c->key);
    c = c->next;
    isf =0;
  }
  printf("\n");
}

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

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

void deleteFirst(){
  struct Node *t = nil->next;
  if(t==nil) return;
  deleteNode(t);
}

void deleteLast(){
  struct Node *t = nil->prev;
  if(t==nil) return;
  deleteNode(t);
}

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

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

int main(){
  int i,n,key;
  int size =0;
  char A[20];
  int np =0,nd =0;
    scanf("%d",&n);
    init();
    for(i=0;i<n;i++){
      scanf("%s%d",A,&key);
      if(A[0]=='i'){
	insert(key);
	np++;
	size++;
      }
      else if(A[0]=='d'){
	if(strlen(A)>6){
       if(A[6]=='F') deleteFirst();
       else if(A[6]=='L') deleteLast();
	}
	else{
	  deleteKey(key);
	  nd++;
	}
	size--;
      }
    }

    printList();

    return 0;
}