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 *prev, *next;
};
struct Node *nil;
void printList(){
  struct Node *cur = nil->next;
  int isf =0;
  while(1){
    if(cur==nil){
      break;
    }
    if(isf++>0){
      printf(" ");
    }
    printf("%d",cur->key);
    cur=cur->next;
  }
  printf("\n");
}
void init(){
        nil=(struct Node *)malloc(sizeof(struct Node));
        nil->next=nil;
        nil->prev=nil;
}
void insert(int key){
        struct Node *x=(struct Node *)malloc(sizeof(struct Node));
        x->key=key;
        x->next=nil->next;
        nil->next->prev=x;
        nil->next=x;
        x->prev=nil;
}
struct Node* listsearch(int key){
        struct Node *cur=nil->next;
        while(cur!=nil&&cur->key !=key) {
                cur=cur->next;
        }
        return cur;
}
void deleteNode(struct Node *t){
        if(t==nil) {
                return;
        }
        t->prev->next=t->next;
        t->next->prev=t->prev;
        free(t);
 
}
void deleteFirst(){
        deleteNode(nil->next);
}
void deleteLast(){
        deleteNode(nil->prev);
}
void deletekey(int key){
        deleteNode(listsearch(key));
}
int main(){
        int key,n,i;
        int size=0;
        char com[20];
        int np=0,nd=0;
        scanf("%d",&n);
        init();
        for(i=0; i<n; i++) {
                scanf("%s%d",com,&key);
                if(com[0]=='i') {
                        insert( key);
                        np++;
                        size++;
                }
                else if(com[0]=='d') {
                        if(strlen(com)>6) {
                                if(com[6]=='F') {
                                        deleteFirst();
                                }
                                else if(com[6]=='L') {
                                        deleteLast();
                                }
 
                        }
 
                        else{
                                deletekey(key);
                                nd;
                        }
                        size--;
 
                }
        }
        printList();
        return 0;
}