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>


struct node{
  int key;
  struct node *next,*prev;

};

struct node *nil;

struct node *search(int);
void init();
void print();
void delnode(struct node *);
void delfirst();
void dellast();
void delkey(int k);
void insert(int key);

int main(){
  int key,i,n,s=0,size=0;
  char a[50];
  int np=0,nd=0;

  scanf("%d",&n);
  init();
  for(i=0;i<n;i++){
    scanf("%s%d",a,&key);
    if(strcmp(a,"insert")==0){
      insert(key);
      np++;    
      size++;
    }else if(a[0]=='d'){
      if(strlen(a)>6){
	if(a[6]=='F') delfirst();
        else if(a[6]=='L') dellast();			
     }else{
          delkey(key);
          nd++;
       }
        size--;
    }
  }
  print();
      
  return 0;
}

struct node *search(int key){
  struct node *nb;
  nb=nil->next;
  while(nb!=nil&&nb->key!=key){
    nb=nb->next;

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

void print(){
  struct node *nb;
  int f=0;
  nb=nil->next;
  while(1){
    if(nb==nil)break;
    if(f++ >0) printf(" ");
    printf("%d",nb->key);
    nb=nb->next;
  }
  printf("\n");

}

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

void delfirst(){
  delnode(nil->next);
}

void dellast(){
  delnode(nil->prev);

}

void delkey(int key){
  delnode(search(key));
}

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